Glossary

Every key term, with the chapter that first defines it. Terms are listed alphabetically.

A

AAFS (American Academy of Forensic Sciences) — the major U.S. professional organization for forensic science (founded 1948), organizing practitioners across the disciplines into sections, holding an annual scientific meeting, publishing a peer-reviewed journal, and promoting standards and education; an umbrella professional society, not a certifying board. (Ch.40)

Accelerant — any substance used to initiate or speed the spread of a fire, most commonly an ignitable liquid such as gasoline; its presence must be confirmed by laboratory analysis and is not, by itself, proof of arson. (Ch.22)

Accident reconstruction — the application of physics and engineering to determine how a collision or other accident occurred — the speeds, paths, positions, and sequence of events — by analyzing the physical evidence (tire marks, crush damage, rest positions, event-data-recorder data) it left behind. (Ch.36)

Accreditation — formal recognition by an independent accrediting body that a laboratory operates a documented quality-management system and is competent to perform the tests within its declared scope; it certifies conformance to a standard, not the correctness of any given result or the scientific validity of the underlying method. (Ch.4)

Accumulated degree days (ADD) — the accumulated thermal energy available for insect development, measured as degrees of temperature above a species' developmental threshold summed over time; used to estimate larval age and thus the minimum postmortem interval. (Ch.13)

ACE-V — the four-step latent-comparison method: Analysis (of the latent alone), Comparison (latent to exemplar), Evaluation (identification / exclusion / inconclusive), and Verification (independent re-examination); a structured framework for a subjective judgment, not an algorithm, with no objective threshold for "enough" agreement. (Ch.14)

AFIS (Automated Fingerprint Identification System) — a computerized system that digitizes a query print, extracts its features (chiefly level 2 minutiae plus pattern class), searches stored records, and returns a ranked candidate list of the most similar records; it generates investigative leads, never identifications, and can prime the examiner who reads the list. (Ch.14)

Age estimation — assessment of age at death from skeletal indicators; precise for subadults (dental development and epiphyseal fusion) but only loosely bounded for older adults, where it must be reported as a wide range because post-growth age markers are slow and individually variable. (Ch.12)

AI/ML in forensics — the use of artificial-intelligence and machine-learning systems (algorithms that learn patterns from large training datasets rather than following explicitly written rules) to perform or assist forensic tasks such as database search, mixture interpretation, deepfake detection, and image comparison; powerful but carrying specific perils — black-box opacity, training-data bias, automation bias, and a pervasive validation gap — that must be evaluated against the NAS/PCAST validity spectrum exactly as any other method. (Ch.29)

Algor mortis — the cooling of the body toward ambient temperature after death; the most quantifiable of the early postmortem clocks, but heavily confounded by body size and fat, clothing, the surface, air movement, humidity, and the unknown ambient history. (Ch.11)

Allele — a specific version found at a locus (for STRs, a particular repeat number); each person carries two alleles at each autosomal locus, one inherited from each biological parent. (Ch.7)

Allele dropout — the failure of a true allele to amplify in a low-template sample, so that a heterozygous locus can appear homozygous or a locus can go blank; its converse, allele drop-in, is the appearance of a spurious allele belonging to no true contributor. (Ch.8)

Allele frequency — the proportion of chromosomes in a reference population that carry a particular allele at a given genetic location; the raw material from which match probabilities are built. (Ch.9)

Analytical microscopy — the use of magnifying optical and (at higher magnification) electron instruments to observe, characterize, and compare the physical and structural features of trace evidence that are invisible or ambiguous to the naked eye. (Ch.23)

Ancestry estimation — the attempt to estimate population affinity from skeletal features (chiefly cranial morphology and measurement); the least accurate and most scientifically and ethically contested component of the biological profile, because socially defined "race" does not map cleanly onto continuous (clinal) biological variation. (Ch.12)

Antemortem records — dental records created during a person's life — radiographs, charts, treatment notes, study models, photographs, and impressions, made by a dentist, orthodontist, oral surgeon, or institutional dental service; the known side of a dental-identification comparison. (Ch.17)

Antemortem/postmortem reconciliation — the systematic, case-by-case comparison of the postmortem record (built from the bodies) against the antemortem record (built on the reported-missing) to establish which body belongs to which missing person; the matching step (Interpol Phase 4) that converts two independent data streams into confirmed identifications. (Ch.35)

Arch — the simplest level 1 pattern: ridges enter one side, rise in the middle, and exit the other side without recurving or forming a circuit; the rarest pattern family. (Ch.14)

Area of origin — the estimated three-dimensional region from which a spatter pattern originated, reconstructed from individual stains' directionality and impact angles (via convergence plus the angle-derived height); a bounded estimate with real uncertainty, never a precise point. (Ch.10)

Asset tracing — the process of following the movement and transformation of funds and property from a source to their current location, performed both to recover stolen or laundered assets and to establish that funds with a particular origin benefited a particular person. (Ch.27)

Audit trail — the chronological, documented record of transactions and process steps, detailed enough to allow each entry to be traced back to its source and forward to its result; in digital systems it includes metadata (who created or modified an entry, and when) that can betray manipulation. (Ch.27)

Autopsy — a thorough, documented postmortem examination of a body to determine the cause and manner of death, establish identity where unknown, and record any findings relevant to a legal investigation; a forensic autopsy is performed for a legal question and documented to be defended in court. (Ch.11)

B

BAC (blood alcohol concentration) — the amount of ethanol in the blood, in the U.S. expressed as grams per 100 mL (written as a percentage); a reliable measurement whose back-calculation to an earlier moment (retrograde extrapolation) rests on attackable assumptions about the absorption–elimination curve. (Ch.20)

Ballistics — strictly, the physics of projectiles in motion, divided into internal (inside the firearm), external (in flight), and terminal (on striking a target); in common forensic usage, the broader discipline of firearms examination, including the comparison of marks on bullets and cartridge cases (which is not, strictly, ballistics at all). (Ch.15)

Barnum effect — (also the Forer effect) the tendency to accept vague, broadly applicable personality descriptions as highly accurate descriptions of oneself (or of an offender); the mechanism by which an uninformative profile feels uncannily specific. (Ch.28)

Bayesian reasoning — a framework for updating the probability of a hypothesis as new evidence arrives, combining a prior probability with the weight of the new evidence (the likelihood ratio) to produce a posterior probability; in forensic terms, posterior odds = LR × prior odds. (Ch.9)

Benford's law — the statistical regularity by which, in many naturally occurring datasets spanning several orders of magnitude, the leading digits follow a decreasing distribution (the digit 1 leads about 30% of the time, the digit 9 only about 5%), given by $P(d) = \log_{10}(1 + 1/d)$; used forensically as a screening tool to flag — never to prove — possible manipulation. (Ch.27)

Bias cascade — the propagation of an expectation or irrelevant piece of context introduced at one point in an investigation through subsequent analyses, verifications, and re-examinations, so that conclusions which appear to independently corroborate one another are in fact a single biased judgment echoing through the system (and growing in confidence as it goes). (Ch.31)

Biological profile — an estimate of a deceased individual's biological sex, age at death, ancestry (population affinity), and living stature derived from the skeleton; it narrows an identification to a class of people but does not, by itself, individualize. (Ch.12)

Bite-mark analysis (debunked) — the discredited claim that an examiner can identify the person who made a patterned bite injury, especially on skin; it rests on premises (unique dentition, faithful recording by skin, reliable examiner comparison) that were asserted but never validated, fails error-rate testing, and has contributed to multiple wrongful convictions (Krone, Brown). (Ch.16)

Blind analysis — performing an examination without knowledge of the suspect's identity, the case theory, the desired outcome, or other examiners' conclusions, so that the analyst's judgment cannot be steered by an expectation it never received; the strongest form of context management. (Ch.31)

Bloodstain pattern analysis (BPA) — the examination of the size, shape, distribution, and location of bloodstains to infer the events, mechanisms, and sequence that produced them; partly grounded in fluid physics but heavily interpretive, and criticized by the 2009 NAS report as often more subjective than scientific. (Ch.10)

Board certification — a credential awarded by an independent professional board attesting that an individual has met defined standards of education, training, and tested competence in a specific forensic discipline and has agreed to a code of ethics and ongoing requirements; it attests to a person's competence in a discipline, not to the scientific validity of the method the person practices. (Ch.40)

C

Cartridge case — the metal cylinder (usually brass) that holds the primer, propellant powder, and seated bullet, and which is ejected when a self-loading firearm fires; it records firing-pin, breech-face, extractor, and ejector marks and is often a richer comparison witness than the bullet. (Ch.15)

Cast — a three-dimensional reproduction of an impression, made by pouring a casting medium (typically dental stone, a hard gypsum product) into a three-dimensional impression and letting it cure into a positive replica of the source for comparison. (Ch.16)

Cause of death — the disease or injury that initiated the lethal sequence of events (the what that killed the person), e.g., "blunt-force head injuries"; usually the firmest of the three death determinations. (Ch.11)

Cell-site/location data — historical records, maintained by a cellular carrier, of which cell towers and sectors a given phone connected to and at what times, used to infer the general geographic area (a tower-sector coverage area, not a GPS point) in which the phone was located. (Ch.25)

Chain of custody — the chronological documentation of the seizure, custody, control, transfer, analysis, and disposition of an item of evidence, recording every handler and every handoff, establishing that the item presented in court is the same item collected at the scene, unaltered in any undocumented way. (Ch.2)

Chromatography — a technique that separates the components of a mixture by exploiting how differently each component distributes between a moving "mobile" phase (a carrier gas in GC, a liquid solvent in HPLC) and a stationary phase; its output is a chromatogram of peaks, each at a characteristic retention time. (Ch.23)

Class characteristic — A property an item shares with all other members of a defined group (for example, a shoe's tread pattern). It narrows the field of possible sources but cannot, by itself, point to one. (Ch.1)

Code of ethics — the written, formal statement of forensic ethical obligations adopted by a professional organization or laboratory, intended to guide conduct and to provide a standard against which misconduct can be measured and disciplined; necessary but not sufficient, because it relies on individual will against structural pressure and assumes good faith. (Ch.38)

CODIS (Combined DNA Index System) — the U.S. national DNA database, administered by the FBI, that searches an unknown crime-scene profile against offender and casework profiles; it stores numerical profiles rather than identities, and produces investigative leads, not verdicts. (Ch.7)

Coerced-compliant confession — a false confession in which the suspect knows they are innocent but confesses anyway to escape an intolerable interrogation or to obtain a promised or implied benefit; the type most common in the wrongful-conviction record, defined by the internal contradiction of saying "I did it" while privately knowing otherwise. (Ch.33)

Coerced-internalized confession — a false confession in which an innocent, often highly stressed suspect comes genuinely to believe — at least temporarily — that they committed the crime, having been persuaded by relentless, confident interrogation and frequently by fabricated evidence that they did it and simply do not remember; the suspect's memory itself is altered under pressure. (Ch.33)

Cognitive bias — the systematic departure of human judgment from what the evidence dictates, produced by the normal operation of mental shortcuts, expectations, and motivation rather than by any conscious intent; systematic means directional (it pushes consistently toward the expected answer), so unlike random error it cannot be averaged away, and unlike a character flaw it cannot be cured by willpower or sincerity. (Ch.31)

Commingled remains — the remains of two or more individuals mixed together, so that body parts and fragments cannot be assumed to belong to a single person and must be re-associated (sorted back to individuals) before or alongside identification. (Ch.35)

Communicating uncertainty — the skill of conveying a forensic finding's true strength and limits to a non-specialist audience, expressing results as strengths of evidence or probabilities rather than certainties, so the factfinder can weigh the evidence correctly; being exactly as confident as the science warrants, neither inflating a result to satisfy the CSI-effect expectation of certainty nor collapsing into uselessly vague hedging. (Ch.30)

Comparison microscope — two compound microscopes joined by an optical bridge so a single eyepiece presents two specimens side by side in one split field of view at matched magnification and lighting; powerful for exclusion and indispensable for fibers, firearms, and toolmarks, but biased toward finding agreement when the examiner knows which specimen is the suspect's. (Ch.19)

Conditional evidence — evidence produced by an event or action and dependent on the conditions at a specific moment (a door's lock state, a body's position, a light on or off, a fire's state on arrival); destroyed the instant those conditions are changed, and so usually preserved by documentation. (Ch.3)

Confidence–accuracy relationship — the weak and conditional link between a witness's expressed certainty and the correctness of their identification: meaningful only for a pristine confidence statement taken at the first identification under fair conditions, and largely worthless once inflated by feedback and repeated retrieval by the time of trial. (Ch.32)

Confirmation — the second, definitive stage: a more specific method resting on a different chemical principle than the screen (typically GC-MS) that identifies the actual compound and usually quantifies it; only a confirmed result is a forensic identification. (Ch.20)

Confirmation bias — the tendency to seek, notice, weight, and remember information that confirms an existing belief or expectation while overlooking, discounting, or rationalizing information that contradicts it; at the bench it is the engine by which a tentative conclusion defends itself, inflating points of agreement and explaining away discrepancies. (Ch.31)

Confirmatory test — a more specific test that establishes, to a high degree of certainty, that a substance is the target (e.g., that a stain is human blood rather than something that merely behaves like blood in a screen). (Ch.10)

Conflict of interest — a situation in which an institutional position, financial stake, personal loyalty, or other interest creates a risk that professional judgment will be improperly influenced; in forensic science it takes three characteristic forms — the embedded analyst, the hired expert ("hired gun"), and the institution — and is most dangerous where interpretation involves judgment under ambiguity. (Ch.38)

Contamination — the introduction of foreign material into a sample, or the transfer of material between samples, at any point from scene to bench; controlled but never eliminated by physical separation, protective equipment, decontamination, blanks, and staff elimination databases, with the goal of making contamination detectable rather than impossible. (Ch.4)

Context management — the deliberate control of the information available to a forensic examiner so that they receive the domain-relevant data needed to perform the analysis while being shielded from the domain-irrelevant context that could bias the result. (Ch.31)

Contextual bias — the distortion of a forensic judgment by domain-irrelevant information from outside the evidence itself (case facts, the suspect's identity or history, a confession, the desired outcome, other examiners' results); often the trigger that supplies the expectation that confirmation bias then pursues. (Ch.31)

Continuing competency — the ongoing professional obligation, through continuing education, periodic proficiency testing, and recertification, to demonstrate that a practitioner's skills remain current and reliable across a career, rather than treating an initial qualification as permanent; the career-long counterpart to laboratory proficiency testing. (Ch.40)

Contributing factors to wrongful conviction — the recurring, identifiable causes that the systematic study of exonerations shows appear repeatedly in cases where an innocent person was convicted — chiefly mistaken eyewitness identification, false confession, flawed or misapplied forensic science, incentivized informants, and official misconduct — which typically combine and reinforce one another rather than acting alone. (Ch.34)

Control sample — material collected to establish a baseline and to prove that a result is attributable to the evidence rather than to the substrate, the reagents, or the collection process; includes substrate (background), reagent (negative), positive, and elimination controls. (Ch.3)

Controlled-substance analysis — the forensic identification of illegal drugs and regulated pharmaceuticals (determining what a seized substance is, and often how much is present); the highest-volume work of a crime laboratory's chemistry section. (Ch.21)

Convergence of evidence — the situation in which multiple independent lines of evidence, each established on its own and each pointing the same way, together support a conclusion no single line could support alone; powerful only to the degree the threads are genuinely independent, since independent improbabilities multiply but dependent ones do not. (Ch.39)

Conviction integrity unit (CIU) — a division within a prosecutor's office dedicated to preventing, identifying, and remedying wrongful convictions by reviewing innocence and serious-error claims in cases the office itself prosecuted; effective only with genuine independence, adequate resources, and the will to overturn the office's own prior convictions. (Ch.34)

Coroner — an official, historically and often still elected, charged with investigating and certifying reportable deaths, whose qualifications are set by statute and may require no medical training, hiring a physician to perform autopsies while retaining certification authority. (Ch.11)

Crime laboratory — a facility, public or private, that examines physical evidence to produce results for use in the legal system, organized into specialized sections (DNA, drug chemistry, toxicology, trace, latent prints, firearms, documents, digital); small labs refer complex work to a larger state crime laboratory. (Ch.4)

Crime scene — any location where a crime may have occurred and where physical evidence of that crime may be found; a working hypothesis about where the relevant past is still legible, not a fixed bounded place. (Ch.2)

Criminal profiling — the inference of an unknown offender's likely characteristics (demographics, personality, background, behavior) from crime-scene and offense evidence; an investigative aid of weak and unproven validity, not a validated method for identifying an offender, and generally not admitted in court as proof of identity. (Ch.28)

Criminalistics — The branch of forensic science concerned with the recognition, collection, identification, and comparison of physical evidence — the "crime lab" disciplines such as prints, fibers, firearms, drugs, and DNA. (Ch.1)

Cross-examination — the questioning of a witness by the opposing attorney (the side that did not call them), designed to test, limit, undermine, or recontextualize the testimony; conducted largely through leading questions, and for forensic evidence it typically attacks certainty, assumptions, bias, and case-specific application rather than the underlying science. (Ch.30)

Custodial recording — the audio-visual recording of an entire custodial interrogation, from the first word to the last, so that an independent record exists of everything said and done; the single most important reform against false confessions, because it lets anyone reconstruct who first stated each incriminating fact and thereby exposes contamination. (Ch.33)

D

Daubert standard — the federal admissibility standard (from Daubert v. Merrell Dow Pharmaceuticals, 1993): under the Federal Rules of Evidence, the trial judge must independently assess whether proposed expert scientific testimony is both relevant and reliable, rather than merely generally accepted. Reliability replaced reputation as the touchstone. (Ch.5)

Debunked fire indicators — the set of once-trusted visual "signs of arson" — crazed glass, alligator charring, low and irregular "pour" patterns, and similar — that controlled fire research has shown to be unreliable because each is produced routinely by ordinary accidental fires. (Ch.22)

Deconvolution — the attempt to separate a mixed DNA profile into the individual profiles of its contributors, or at least to assess whether a given person could be among them. (Ch.8)

Deepfake — synthetic or manipulated media (most often video or audio) generated or altered by machine-learning techniques to depict a real person saying or doing something they did not, with realism that can be difficult to detect; contrasted with a cruder "cheapfake" made by simple non-AI edits. (Ch.26)

Defense fallacy — the error of dismissing strong evidence by noting that, in a large population, many people would coincidentally match, and concluding the match is therefore nearly worthless, while ignoring the other evidence that placed this particular defendant before the court. (Ch.9)

Dental charting — the standardized, tooth-by-tooth, surface-by-surface notation of the state of the dentition (present, missing, or restored, and how) that allows two records made by different people, in different places, years apart, to be compared like to like. (Ch.17)

Dental identification — establishing the identity of a deceased person by comparing antemortem dental records to a postmortem examination of the dentition, reaching a conclusion of identification, possible/consistent, insufficient, or exclusion. (Ch.17)

Digital evidence — information of evidentiary value stored or transmitted in digital form, including messages, files, location records, app data, and the large layer of automatically generated records (such as metadata) that a user never deliberately creates. (Ch.25)

Digital forensics — the application of scientific methods to the identification, preservation, acquisition, examination, and interpretation of data stored on or transmitted by digital devices, in a manner suitable for use as evidence in a legal proceeding. (Ch.25)

Direct examination — the questioning of a witness by the attorney who called that witness, in which the witness presents their substantive evidence; conducted largely through open-ended questions, and for an expert the part where the opinion and its basis are taught to the jury — and where the chief danger is overstatement invited by the friendly side. (Ch.30)

Disaster victim identification (DVI) — the organized, standardized, multi-disciplinary forensic process for recovering, examining, and identifying large numbers of the dead from a mass-fatality event, and returning them to their families; the same evidentiary discipline (fingerprints, dental, DNA) applied at a scale that overwhelms the routine system. (Ch.35)

DNA (deoxyribonucleic acid) — the molecule that carries genetic instructions, present and identical in nearly every nucleated cell of a single individual; the basis of forensic genetic identification. (Ch.7)

DNA mixture — a biological sample containing DNA from two or more contributors, producing more alleles at a locus than any single person can possess. (Ch.8)

DNA profile — the complete set of alleles a sample shows across all tested loci; the numerical "fingerprint" compared between an evidence sample and a reference. (Ch.7)

Documentation — the systematic creation of a permanent, objective record of a scene as it was found, before anything is disturbed; in crime-scene work, the three independent records of contemporaneous notes, photography, and a measured sketch. (Ch.2)

Double-blind administration — a lineup procedure in which neither the witness nor the administrator knows which member is the suspect, so the administrator cannot consciously or unconsciously steer the witness or give confirming feedback. (Ch.32)

E

Electropherogram — the visual readout of a DNA profile produced by capillary electrophoresis: a graph of fluorescence versus DNA-fragment size in which each allele appears as a peak. (Ch.7)

Enhancement (limits) — image/video operations (brightness, contrast, sharpening, noise reduction, frame averaging on static scenes, geometric correction) that make information already present easier to perceive; enhancement can clarify what the sensor captured but can never add detail that was not recorded — making "zoom-and-enhance" and hallucinated machine "super-resolution" detail false. (Ch.26)

Environmental forensics — the application of scientific methods to determine the source, age, and responsible party of environmental contamination (what a pollutant is, where it came from, and when it was released), in support of regulatory enforcement, litigation, and cleanup-cost allocation. (Ch.36)

Error level analysis (ELA) — an authentication screening technique that re-saves a JPEG at a known compression level and maps the pixel-by-pixel difference, on the theory that edited regions compress differently; a hint toward regions to examine, heavily confounded by edges, text, and texture, and useless on multiply-saved or non-JPEG images — not a standalone proof of manipulation. (Ch.26)

error rate — the frequency with which a method produces a wrong result (false positive or false negative); a known, measured error rate, established by studies against known ground truth, is a core Daubert reliability factor, and its absence is itself a finding. ("We've never been caught wrong" is not an error rate.) (Ch.5)

ESDA — electrostatic detection apparatus (also electrostatic detection device, EDD); a non-destructive instrument that visualizes indented writing by developing the patterns of electrostatic charge held differently by the indentations than by the undisturbed paper surface. (Ch.18)

Estimator vs. system variables — estimator variables are the witnessing conditions (lighting, distance, exposure time, stress, weapon focus, cross-race, retention interval) that the justice system can only estimate after the fact and cannot change; system variables are the controllable choices about how the identification is collected (lineup composition, instructions, administrator, confidence recording, feedback). (Ch.32)

Evidence from the living — evidence recovered from a person who is alive, conscious, and entitled to direct what is done to their own body, so that every step of collection is subject to ongoing, informed, revocable consent and must be performed in a way that minimizes physical and psychological harm. (Ch.37)

Exclusion matrix — a structured grid arraying each person of interest against each line of evidence, recording for each cell whether the evidence excludes, is consistent with, or does not apply, so that the field is narrowed by what the science can rule out before anyone reasons about who remains. (Ch.39)

Exemplar — a sample of known writing used as the standard of comparison against a questioned document; collected (non-request) exemplars are produced in the ordinary course of life before any dispute, while requested (dictated) exemplars are produced on demand, typically by dictation. (Ch.18)

Exoneration — the official undoing of a conviction (by pardon, dismissal of charges, or acquittal on retrial) on the ground that the convicted person did not commit the crime. (Ch.6)

Exoneree — a person who was convicted of a crime and later officially cleared of it; the human being to whom an exoneration (the official act, Ch.6) happens. (Ch.34)

Expert witness — a witness permitted, by virtue of specialized knowledge, skill, experience, training, or education, to offer opinions and conclusions (not merely firsthand observations) to help the jury understand evidence or determine a fact in issue; the one category of witness the law allows to say what evidence means, and therefore the one most at risk of being over-trusted on authority alone. (Ch.30)

Explosives residue — the trace chemical material left after an explosion or by handling an explosive (unconsumed explosive, characteristic breakdown products, and primer or propellant traces), recoverable in microscopic quantities from a scene, debris, or a suspect's person or environment; meaningful only against rigorous control samples, and a statement about a substance rather than (by itself) a person. (Ch.21)

Eyewitness identification — a witness's report that a particular person is the one they saw commit a crime (or be present at it); persuasive to juries but, because human memory is reconstructive, among the least reliable forms of evidence and a leading documented cause of wrongful conviction. (Ch.32)

F

Failure analysis — the systematic process of determining how and why a structure, component, or system failed, by examining the physical evidence of the failure (fracture surfaces, deformation, materials testing) and reasoning backward to a cause through hypotheses tested against the evidence. (Ch.36)

False confession — an admission of guilt, made to authorities, for a crime the person did not in fact commit, whether a full narrative account of the offense or a briefer acceptance of responsibility; a documented and recurring contributing cause of wrongful conviction. (Ch.33)

Familial searching — the deliberate search of a criminal DNA database (CODIS) for a partial match to a crime-scene profile, on the theory that a close biological relative (parent, child, or full sibling) of a known offender already in the database may be the true source of the crime-scene DNA; uses the same STR markers and the same criminal database as ordinary searching but applies kinship statistics to flag near-misses, and is distinct from investigative genetic genealogy in its markers (STR, not SNP), its database (criminal, not consumer), and its reach (close kin, not distant cousins). (Ch.29)

Fiber — the smallest unit of a textile, either natural (plant or animal, e.g., cotton, wool) or manufactured/synthetic (polymer, e.g., nylon, polyester); class evidence whose forensic value rests on objective measurement (polymer type, cross-section, diameter, color spectrum) and on the rarity of the fiber and the number of independent transfers. (Ch.19)

File carving — the recovery of files from raw, unallocated disk space by recognizing the files' own internal structure (characteristic header and footer byte patterns) independent of any filesystem record; recovers file content but usually strips its original filename, timestamp, and context. (Ch.25)

Fire investigation — the discipline of determining a fire's origin, cause, and development through systematic, scientific-method-based examination of the scene and physical evidence; governed in modern practice by the NFPA 921 standard. (Ch.22)

Flashover — the near-simultaneous ignition of all exposed combustible surfaces in an enclosed space, driven by radiant heat from the accumulated hot-gas layer (often around $500\text{–}600^{\circ}\text{C}$ at the ceiling); it produces low, floor-level, "pour-shaped" burn patterns in ordinary accidental fires, dissolving the old arson indicators. (Ch.22)

Footwear impression — the recorded outline and tread detail left by the underside of a shoe; carries class characteristics (tread design, size, general wear pattern) and acquired/individual characteristics (randomly acquired cuts, gouges, holes, and lodged debris). (Ch.16)

Forensic accounting — the application of accounting, auditing, and investigative skills to financial questions that a legal proceeding must answer; an investigative reconstruction of a person's or company's financial history, distinct from a routine assurance audit. (Ch.27)

Forensic anthropology — the application of physical/biological anthropology and human skeletal biology to legal questions, especially the recovery, identification, and analysis of decomposed, skeletonized, burned, or fragmentary human remains; the anthropologist supplies skeletal findings, while the pathologist/medical examiner determines cause and manner of death. (Ch.12)

Forensic botany — the application of plant science (identification and analysis of plants, plant fragments, seeds, wood, algae, and especially pollen) to legal questions, chiefly to associate a person or object with a place. (Ch.13)

Forensic career paths — the distinct professional routes through forensic practice (laboratory bench analyst by discipline, crime-scene investigator, forensic pathologist and medicolegal death investigator, digital forensic examiner, consulting specialists such as anthropologists and odontologists, and the laboratory directors and quality staff who oversee them), each with its own education, daily work, certifying body, and role in the justice system — collectively performing the functions that television compresses into a single "forensic scientist." (Ch.40)

Forensic case assembly — the systematic gathering and combined evaluation of every item of evidence in a case, each stated at its true evidentiary strength, to reach the most defensible overall conclusion and to mark that conclusion's limits; distinct from a summary, which restates rather than weighs. (Ch.39)

Forensic chemistry — the application of analytical chemistry to legal questions, chiefly the identification and characterization of substances whose identity matters to an investigation: controlled drugs, explosives and their residues, fire accelerants, and unknown materials. (Ch.21)

Forensic engineering — the application of engineering principles and methods to investigate the causes of failures of structures, materials, components, vehicles, and products, typically when those failures cause injury, death, or significant loss and the cause must be established for legal proceedings. (Ch.36)

Forensic entomology — the application of the study of insects and other arthropods to legal questions, especially estimating the minimum time since death and detecting body movement, drugs/toxins in tissue, or neglect of a living victim. (Ch.13)

Forensic ethics — the set of moral obligations governing the practice of forensic science: the duties to scientific accuracy, impartiality, the people whose liberty depends on the result, and the legal system as a whole, that constrain what an analyst may do, claim, and testify to, especially under pressure to reach a particular answer. (Ch.38)

Forensic imaging — the creation of a complete, bit-for-bit copy of a storage device — every sector, including deleted and hidden regions — so that all analysis is performed on the copy while the original is preserved untouched. (Ch.25)

Forensic isotope analysis — the measurement of the ratios of stable (non-radioactive) isotopes of common elements (hydrogen, oxygen, carbon, nitrogen, sulfur, strontium) in biological tissues to infer an individual's geographic origin, travel history, and diet; because tissues form and turn over at different rates (tooth enamel in childhood, hair over recent months, bone over years), a single body can carry a layered life-history record, yielding a regional investigative lead rather than an identification. (Ch.29)

Forensic nursing — the practice of nursing applied to patients affected by violence, trauma, or other matters that intersect the legal system; the forensic nurse provides health care while recognizing, documenting, collecting, and preserving evidence, and is prepared to communicate findings to courts. Its defining feature is holding medical care and evidence collection as co-equal, deliberate goals of a single encounter. (Ch.37)

Forensic odontology — the application of dental science to legal questions; centrally the identification of human remains from dental records (a valid, reliable contribution), as distinguished from bite-mark comparison (a discredited application owned by Chapter 16). (Ch.17)

Forensic pathology — the branch of medicine that applies pathology (the study of disease and injury in the body) to legal questions, chiefly determining the cause and manner of death in cases that fall under legal jurisdiction. (Ch.11)

Forensic psychology — the application of psychological science and clinical practice to questions a legal system must answer, chiefly the assessment of competency to stand trial, criminal responsibility (sanity), and violence risk in examinable individuals. (Ch.28)

Forensic reform — the structural, scientific, and procedural agenda proposed by the 2009 NAS and 2016 PCAST reports and the reform movement (independence, validation before admission, blind testing and context management, mandatory accreditation, honest standardized reporting, and active judicial gatekeeping) to put forensic science on a sound scientific and ethical footing; much of it, especially the reforms that restructure power, remains unimplemented. (Ch.38)

Forensic science — The application of scientific methods and principles to questions that a court of law must answer; literally "science for the forum." (Ch.1)

Forensic toxicology — the application of the science of poisons (drugs, alcohol, and other chemicals) and their effects on the body to legal questions, comprising the identification of substances, their quantitation, and the interpretation of what a concentration means. (Ch.20)

Forgery — a document or signature fabricated or executed to deceive by imitating a genuine one; recognized categories include the traced forgery, the simulated (freehand) forgery, the disguised writing (genuine writing altered by its own author), and the spurious (blind) forgery that makes no attempt to imitate. (Ch.18)

Fraud examination — the structured process of resolving an allegation of fraud from inception to disposition by gathering evidence, interviewing, reporting, and (where needed) testifying; it begins from an allegation and an investigative mindset rather than an auditor's presumption of good faith. (Ch.27)

FRE 702 — Federal Rule of Evidence 702, governing the admissibility of expert testimony; as amended, it requires that such testimony rest on sufficient facts, be the product of reliable principles and methods, and reflect a reliable application of those methods to the facts of the case. (Ch.5)

Friction ridge — the raised, continuous ridges of hairless skin on the fingers, palms, soles, and toes (with furrows between them), formed before birth, permanent for life barring deep dermal scarring, and bearing the detail used in fingerprint comparison. (Ch.14)

Frye standard — the older U.S. admissibility test (from Frye v. United States, 1923): novel scientific evidence is admissible only if the underlying method has gained general acceptance in its relevant scientific field. Modest and administrable, but blind to a unanimously believed error; still used in some states. (Ch.5)

FTIR (Fourier-transform infrared spectroscopy) — an analytical method that identifies a substance by measuring how it absorbs infrared light; because each type of chemical bond absorbs at characteristic frequencies (vibrating like a tuned spring), the resulting absorption spectrum is a structural fingerprint of the molecule, obtained non-destructively. (Ch.23)

G

gatekeeper — the trial judge's role under Daubert: making the threshold, pre-jury determination of whether proposed expert testimony is reliable enough to be heard at all. The gatekeeper is a generalist judge, not a scientist. (Ch.5)

GC-MS (gas chromatography–mass spectrometry) — a combined analytical instrument in which a gas chromatograph first separates a mixture into its individual components and a mass spectrometer then identifies each component by breaking its molecules into charged fragments and measuring their masses; the combination of a retention-time match and a matching mass spectrum (against a same-day standard) is the forensic gold standard for confirming a compound's identity. (Ch.23)

Gunshot residue (GSR) — the particulate and chemical debris produced by the discharge of a firearm (burned and unburned propellant plus condensed primer particles), deposited on the shooter, on nearby surfaces, and on the target; its presence on a person establishes that residue is present, not that the person fired a weapon. (Ch.24)

H

Hair morphology — the microscopic structure of a hair (the outer cuticle of overlapping scales, the bulk cortex carrying pigment, and the central medulla) and the features these layers present; from it an examiner can read class characteristics such as human-vs-animal origin, body region, and treatment — but not the individual source. (Ch.19)

Handwriting comparison — the examination of questioned writing against known exemplars to assess whether they were produced by the same hand; able to exclude a writer and to detect simulation, but contested as a means of individualizing a writer to the exclusion of all others. (Ch.18)

Hash value — a fixed-length string produced by running data through a one-way cryptographic function; it acts as a digital fingerprint, in that identical inputs always produce the same value, any single-bit change alters it completely, and it cannot feasibly be reversed or forged — used to prove that data has not been altered. (Ch.25)

Hired-gun problem — the risk that an expert witness, because retained and paid by one party in an adversarial contest, will (often unconsciously, via adversarial allegiance) shade their opinions toward the conclusion that party needs, becoming an advocate for a side rather than a neutral witness for the truth; the structural pressure against which the expert's overriding duty is to the court, not the client. (Ch.30)

I

Ignitable-liquid residue (ILR) — the detectable chemical remnants of an ignitable liquid recovered from fire debris and identified by laboratory instrumentation (GC-MS); strong evidence of an accelerant when present, but its absence does not prove that none was used. (Ch.22)

Image authentication — the process of determining whether an image or video is genuine and unaltered and is what it purports to be (captured by the claimed device, time, and place), or has been manipulated, fabricated, or mislabeled; built from converging indicators, no single one a verdict alone. (Ch.26)

Image forensics — the application of scientific methods to the analysis, measurement, and authentication of images and video for legal purposes (as distinct from the "zoom-and-enhance" fantasy of television). (Ch.26)

Immunoassay — a screening test using antibodies that bind a target drug or drug class to produce a measurable signal; fast and inexpensive but prone to cross-reactivity (false positives from structurally similar substances), and therefore presumptive only. (Ch.20)

Impression evidence — physical evidence in which the shape of one object is transferred to, and recorded on, the surface of another (footwear, tire, tool, or bite); governed by the class-versus-individual comparison logic of Chapter 1 and a legible form of Locard's exchange principle. (Ch.16)

Indented writing — the pressure impression left in a sheet of paper by writing on a sheet that lay above it; recoverable even after the upper sheet (and its ink) is gone, because the impression is physically present in the surviving page. (Ch.18)

Individual characteristic — A property believed to be effectively unique to a single source (for example, the random wear and damage on one used shoe). It can strongly associate evidence with that specific source. (Ch.1)

Individualization — The claim that a piece of evidence originated from one specific source to the exclusion of all others in the world. Demonstrable for quantified DNA, but an overstated assumption for most pattern-comparison methods. (Ch.1)

Interpol DVI phases — the five-phase international framework that organizes a mass-fatality identification — (1) the scene, (2) postmortem examination, (3) antemortem data collection, (4) reconciliation, (5) debriefing — and that keeps the postmortem and antemortem data streams separate until reconciliation. (Ch.35)

Interrogation vs. interview — the distinction between an accusatory, guilt-presumptive process aimed at obtaining a confession from a person the questioner has already concluded is guilty (interrogation) and a non-accusatory, open-ended process aimed at gathering information (interview); only the latter has a mechanism for recognizing that it has the wrong person. (Ch.33)

Investigative genetic genealogy (IGG) — the technique of generating a dense SNP profile from crime-scene DNA, finding distant relatives in a consumer genealogy database, and reconstructing family trees to develop an investigative lead that conventional STR typing then confirms. (Ch.8)

ISO/IEC 17025 — the international standard ("General requirements for the competence of testing and calibration laboratories") specifying what a competent testing laboratory must have in place; the standard most crime laboratories are accredited to. (Ch.4)

J

Junk science — a method or claim presented in court as valid science despite lacking a demonstrated scientific basis: no measured error rate, no validated procedure, and no foundation beyond practitioner confidence; misleads even an honest examiner. (Ch.6)

K

Kastle-Meyer — the classic presumptive blood test using reduced phenolphthalein plus hydrogen peroxide, turning pink when blood's heme/peroxidase activity is present; highly sensitive but not specific, and false-positive on some plant peroxidases and oxidizers. (Ch.10)

Known sample — material from a verified, documented source, collected so that a questioned sample can be compared against it; its defining feature is that its origin is certain. Also called a reference sample. (Ch.3)

Kumho Tire — Kumho Tire Co. v. Carmichael (1999): the U.S. Supreme Court decision extending the judge's Daubert gatekeeping duty to all expert testimony — technical and experience-based, not only self-described "scientific" testimony — closing the loophole for pattern disciplines that recharacterized their work as skill rather than science. (Ch.5)

L

Lab independence — structural separation of the forensic laboratory from the law-enforcement and prosecution agencies that have a stake in its results; its absence (most U.S. labs being administratively embedded within those agencies) produces structural bias toward the prosecution and is the 2009 NAS report's deepest and least-adopted recommendation. (Ch.38)

Lands and grooves — the raised metal between the spiral channels (lands) and the cut-away spiral channels themselves (grooves) of a rifled barrel; their number, width, and direction/rate of twist are class characteristics readable from a fired bullet. (Ch.15)

Latent print — an invisible friction ridge impression left by the natural residue (sweat, oils, salts, amino acids) on the skin, requiring development to be made visible; in common usage, the working term for crime-scene prints generally. (Ch.14)

Lethal range — the band of concentrations associated with death; even a finding here is an interpretation (tolerance and drug combinations can shift it), not an automatic verdict of fatal intoxication. (Ch.20)

Level 1 detail — the overall ridge flow and pattern class (loop, whorl, arch); a class characteristic that can exclude a source or narrow the field, but can never identify. (Ch.14)

Level 2 detail — the minutiae; the principal basis of a fingerprint identification. (Ch.14)

Level 3 detail — features within a single ridge (ridge-edge shape, sweat-pore positions, ridge width, incipient ridges); adds discriminating power in high-quality prints but is fragile and highly sensitive to how the print was deposited. (Ch.14)

Likelihood ratio (LR) — a number expressing how much more (or less) probable the observed evidence is under one hypothesis than under a competing hypothesis; in forensic DNA, the probability of the results if the defendant is a contributor divided by the probability of the same results if an unknown, unrelated person is. An LR of 1 million means the evidence is one million times more probable under the prosecution's proposition than under the defense's. (Ch.9)

Lineup — a formal identification procedure in which a witness views the suspect together with known-innocent fillers (live or, more commonly, as a photo array) and is asked whether they recognize the perpetrator; distinct from a single-suspect showup. (Ch.32)

Livor mortis — the gravity-driven purplish-red discoloration (postmortem hypostasis/lividity) that settles in the dependent parts of the body after the heart stops; becomes fixed after roughly 8–12 hours, can reveal that a body was moved, and can hint at cause (cherry-red in carbon-monoxide poisoning or cold). (Ch.11)

Locard's exchange principle — the principle that whenever two objects come into contact there is a mutual transfer of material between them; popularly, "every contact leaves a trace" (and takes one). It guarantees that a trace is deposited, not that it will be detected, persist, be distinguishable from its background, or answer the question being asked. (Ch.3)

Locus — a specific, named physical location in the genome that forensic scientists agree to target for typing; plural loci. (Ch.7)

Loop — a level 1 pattern in which one or more ridges enter from one side, recurve, and exit the same side; the most common pattern family. (Ch.14)

Low-template DNA — DNA present in very small quantity (a few cells / picogram amounts), below standard validation levels, where the random nature of early amplification produces stochastic distortions in the profile. (Ch.8)

Luminol — a presumptive blood reagent that chemiluminesces (glows blue in darkness) in the presence of heme; reveals latent and cleaned-up bloodstains but false-positives on bleach and oxidizing cleaners, metal ions, and plant peroxidases, and can degrade DNA. (Ch.10)

M

Manner of death — the category of circumstances by which the cause came about — natural, accident, suicide, homicide, or undetermined; a reasoned medical opinion built from the autopsy plus the scene and history, and revisable when new information arrives. (Ch.11)

Mass fatality — any event that produces more dead than the local death-investigation system can manage with its routine resources and procedures; defined by the system being overwhelmed rather than by a fixed body count. (Ch.35)

Mass spectrum — a plot of the relative abundance of the charged fragments a molecule breaks into when ionized, arranged by their mass-to-charge ratio (m/z); because a molecule fragments in a reproducible, structure-specific way, the pattern serves as a near-definitive identification of the compound, and the heaviest major peak (the molecular ion) gives its molecular weight. (Ch.23)

Mechanism of death — the physiological derangement (e.g., exsanguination, cardiac arrhythmia, hypoxia) that the cause produces and that actually ends life; the least useful of the three for the legal question, since many different causes share a mechanism. (Ch.11)

Medical examiner — an appointed physician, in the strongest systems a board-certified forensic pathologist, given legal authority to investigate and certify reportable deaths on medical and scientific grounds. (Ch.11)

Metabolite — a product the body makes when it chemically transforms a substance, usually en route to eliminating it; its presence indicates the parent drug was in the body and was processed, even after the parent drug itself is no longer detectable. (Ch.20)

Metadata — data that describes other data: information about a file rather than its visible content (for example, a file's creation/modification/access timestamps, its registered author, or the camera settings and embedded GPS coordinates of a photograph); often forensically powerful because it is generated automatically, but it records device events rather than necessarily a person's actions. (Ch.25)

Method validation — the documented testing of an analytical method against samples of known truth, before any casework, to establish its accuracy, precision, sensitivity, specificity, robustness, and error rate; developmental validation proves a method can work in principle, internal validation proves that a particular laboratory can run it correctly. (Ch.4)

Microbial forensics — the application of the analysis of microbial communities (bacteria and other microorganisms) to legal questions, including estimating the postmortem interval from the necrobiome, associating a person with a place or object through transferred skin microbes, and attributing a deliberate biological attack to its source; an emerging field whose underlying sequencing science is sound but whose forensic validation, for most uses, is incomplete. (Ch.29)

Microcrystalline test — a presumptive technique in which a reagent added to a trace of the suspected substance on a microscope slide causes the target compound to form crystals of a characteristic shape and habit, read by the analyst under magnification; more discriminating than a color test but still presumptive and partly subjective. (Ch.21)

Microscopic hair comparison — the visual comparison of a questioned and a known hair under a microscope to opine on a possible common source; a method that can support exclusion (and the triage of hairs to DNA) but cannot identify a person, and whose strong forms — notably the FBI's pre-2000 testimony — were found scientifically unsupported and systematically overstated by the 2015 review. (Ch.19)

Minutiae — the individualizing level 2 features where friction ridges end, split (bifurcate), form dots, or combine (enclosures, spurs, crossovers); their configuration — relative position, type, orientation, and ridge counts between them — not their count alone, carries identification value. Historically called "Galton points." (Ch.14)

Modus operandi (MO) — the learned, functional behaviors an offender uses to commit a crime and avoid detection; because it serves the practical goal of completing the offense, it tends to evolve with experience. (Ch.28)

Money laundering — the process of disguising the illegal origin of criminally derived funds, conventionally through placement (introducing cash into the financial system), layering (moving it through complex transactions to obscure its origin), and integration (returning it to the economy as apparently legitimate funds), so the money can be used freely. (Ch.27)

mtDNA (mitochondrial DNA) — the small, circular, high-copy-number genome carried in the mitochondria and inherited maternally; recoverable from degraded or rootless samples that defeat nuclear typing, but shared along a maternal line and therefore unable to individualize. (Ch.8)

N

NAS 2009 report — the National Academy of Sciences report Strengthening Forensic Science in the United States: A Path Forward (2009), which found that, apart from nuclear DNA analysis, the forensic disciplines lacked rigorous validation, called the field "badly fragmented," and recommended sweeping reform. (Ch.6)

Necrobiome — the community of organisms (especially microbial) that participates in the decomposition of a body and changes in a characteristic, time-dependent sequence after death; proposed as a microbial cousin of insect succession for estimating the postmortem interval, but highly sensitive to temperature, soil, moisture, and individual variation. (Ch.29)

Negative corpus — the discredited reasoning (rejected by NFPA 921) that classifies a fire as incendiary purely by eliminating identified accidental causes rather than from affirmative evidence of a deliberately set fire; the honest classification when the cause cannot be affirmatively established is "undetermined." (Ch.22)

NIBIN/IBIS — the National Integrated Ballistic Information Network (the U.S. database, administered by the ATF) and its Integrated Ballistics Identification System imaging engine; it captures and correlates images of cartridge-case and bullet marks to generate ranked investigative leads for a firearms examiner to confirm or reject, not courtroom matches. (Ch.15)

O

Origin and cause — the linked central questions of fire investigation: where a fire began (the origin) and what started it (the cause); the cause cannot be reliably determined without first correctly establishing the origin. (Ch.22)

OSAC (Organization of Scientific Area Committees for Forensic Science) — a body administered by the National Institute of Standards and Technology (NIST) that coordinates the development of consensus-based scientific standards and guidelines across the forensic disciplines and maintains a registry of standards it judges sound; it can recommend standards but, by design, cannot compel laboratories to adopt them. (Ch.38)

P

Paint-layer comparison — the examination and comparison of the number, sequence, color, thickness, and chemical composition of the individual layers in a questioned paint sample against a known sample, to assess a possible common origin; the probabilistic weight lies in the matching sequence, and a multi-layer match (especially with unusual layers) can strongly support a common origin without individualizing. (Ch.24)

Palynology — the study of pollen and spores; in forensics, the comparison of pollen and spore assemblages from an item to the plant community of a location, to associate the item with a place of that flora. (Ch.13)

Patent print — a visible friction ridge impression left when the finger transfers a colored or contaminating substance (blood, ink, grease, paint, dust) to a surface. (Ch.14)

PCAST 2016 report — the President's Council of Advisors on Science and Technology report on feature-comparison methods (2016), which introduced the distinction between foundational validity (does the method work, by empirical study?) and validity as applied, and judged which methods met the bar. (Ch.6)

PCR (polymerase chain reaction) — a laboratory technique that copies a targeted DNA region exponentially, turning a trace amount into billions of copies; the basis of modern STR typing and the origin of its sensitivity-driven contamination risk. (Ch.7)

peer review — independent scrutiny of a method or result by experts who did not develop it, typically as a condition of scientific publication; a Daubert factor and a marker (not a guarantee) that a method has been exposed to outside criticism rather than circulating only among its own practitioners. (Ch.5)

Perimortem trauma — injury inflicted at or near the time of death, on fresh, moist, elastic bone with no time to heal; recognized by curved, beveled fractures of the same color as the surrounding bone, and the trauma category that bears on cause and manner of death. (Ch.12)

Photogrammetry — the science of obtaining reliable real-world measurements (especially a person's height) from photographs or video by reconstructing the geometry of the camera's projection; most defensibly via reverse projection, in which a known reference is imaged at the same stand point with the same camera so lens and angle cancel. (Ch.26)

Physical evidence — any tangible object or material that can establish, through scientific examination, that a crime occurred or that connects (or excludes) a person, place, or thing in relation to the crime. (Ch.3)

Plastic print — a three-dimensional friction ridge impression pressed into a soft, moldable material (putty, wax, soft caulk, tacky adhesive) that holds the shape. (Ch.14)

Post-conviction review — the legal and investigative processes by which a conviction, already final and past its ordinary appeals, is reexamined for error; the obstructed channel through which an exoneration must travel, distinct from the ordinary appeal that tests process rather than factual innocence. (Ch.34)

Postmortem interval (PMI) — the time elapsed since death, estimated in the early window from livor, rigor, and algor mortis and from decomposition, and always reported as a range rather than a single moment. (Ch.11)

Postmortem records — the dental examination, charting, and radiographs the forensic odontologist creates from the body; the questioned side of the comparison, made (where practical) independently before the antemortem records are studied in detail. (Ch.17)

Postmortem toxicology — the analysis and interpretation of drugs and poisons in the deceased, distinguished from the toxicology of the living by postmortem changes (redistribution, alcohol neoformation, drug instability) that make a corpse's chemistry an unreliable mirror of the antemortem state unless carefully accounted for. (Ch.20)

Postmortem trauma — damage to bone occurring after death, to dry, brittle bone; recognized by straight, transverse, squared, often off-color fractures, and forensically important because it must not be mistaken for perimortem injury. (Ch.12)

Presumptive color test — a chemical screening test in which a reagent produces a characteristic color (or sequence of colors) when it contacts a class of substance, indicating the class is probably present, or — when negative — probably absent; class-level and fallible, and never, by itself, an identification. (Ch.21)

Presumptive test — a fast, sensitive, inexpensive screening test indicating a substance is probably present (and reliably indicating where it is absent); never an identification by itself because non-target substances can trigger a positive. (Ch.10)

Primary scene — the location where the principal criminal act occurred (e.g., where the victim was killed). (Ch.2)

Primer residue — the inorganic particulate component of gunshot residue, formed when the metallic primer compounds (most commonly lead, barium, and antimony) are vaporized on discharge and condense into characteristic spheroidal particles; the diagnostic particle contains the right elements in the right morphology and is identified by SEM-EDX. (Ch.24)

Probabilistic genotyping — a class of software that uses explicit statistical models and computational methods to interpret DNA profiles, especially complex or low-template mixtures, by computing a likelihood ratio rather than relying on an analyst's subjective peak-by-peak judgment. (Ch.9)

Proficiency testing — a formal exercise in which an analyst is tested on samples whose correct answers are known to the provider, to measure competence; most revealing when blind (introduced into the casework stream disguised as a real case) and weakest when the analyst knows it is a test or the samples are unrepresentatively easy. (Ch.4)

Prosecutor's fallacy — the error of treating the probability of the evidence given innocence (e.g., the random match probability) as if it were the probability of innocence given the evidence; a transposed conditional that confuses coincidence with guilt. (Ch.9)

Provenance — the documented origin and history of a digital file (its source device, capture time and place, and edit history), carried fragilely by metadata (e.g., EXIF) and, increasingly, durably by cryptographic content-authentication standards that sign media at capture and track subsequent edits. (Ch.26)

Q

QA/QC — the combined quality system of a laboratory: quality assurance, the proactive system-level policies, procedures, training, and audits that ensure quality before and around the work, and quality control, the operational sample-by-sample checks (positive controls, negative controls, reagent blanks) that verify a given analysis actually worked. (Ch.4)

Questioned document — any document whose source, authenticity, or history is in dispute and is therefore the subject of forensic examination; "document" includes not only the writing but the medium (paper, ink, toner) and the impressions pressed into it. (Ch.18)

R

Random match probability (RMP) — the probability that a randomly chosen, unrelated person from the relevant population would coincidentally share the evidence profile; it states the rarity of a match, not the probability of a suspect's innocence. (Ch.7)

Rapid DNA — the fully automated generation of a short-tandem-repeat (STR) profile from a reference sample (typically a buccal swab) inside a single self-contained instrument, without a human analyst performing the steps, in roughly 90 minutes to two hours; validated for clean, single-source reference samples (and, under the Rapid DNA Act of 2017, for approved arrestee-swab CODIS searching), but not for complex, degraded, or mixed evidentiary samples, which require laboratory interpretation. (Ch.29)

Reference sample — a known sample collected specifically for comparison against a questioned item (e.g., a buccal swab from a suspect, reference fibers from a garment); its source and provenance are documented and certain. (Ch.3)

Refractive index (glass) — a measure of how much a material bends (slows) light passing through it, measured very precisely on tiny glass fragments; a powerful tool for excluding a common source (different index = different source), but only a weak associator because float glass is mass-produced within a narrow index range. (Ch.24)

Reid technique — a structured, multi-step, guilt-presumptive interrogation method (developed and trademarked by John E. Reid and Associates) built on isolating the suspect, confronting them with confident assertions of guilt, refusing to accept denials, and offering psychologically framed minimizing "themes" to make confession easier; effective at obtaining admissions and, in the view of a growing body of research, structurally prone to producing false confessions from the innocent. (Ch.33)

Rifling — the series of spiral grooves cut or formed into the interior of most firearm barrels to spin and gyroscopically stabilize the bullet for accuracy; in the process it engraves class and individual marks onto every bullet fired. (Ch.15)

Rigor mortis — the postmortem stiffening of the muscles caused by loss of the energy molecule needed to release them; follows a predictable onset-development-resolution arc that is accelerated by heat and pre-death exertion and slowed by cold. (Ch.11)

S

SANE (Sexual Assault Nurse Examiner) — a registered nurse with specialized education and clinical preparation to provide comprehensive, trauma-informed care to sexual-assault patients, including the medical-forensic examination, evidence collection, and expert testimony. (Ch.37)

Scene security — the set of actions that restrict access to a scene (perimeter, access control, and an entry/exit log) so that evidence is neither lost, added, moved, nor contaminated before it can be documented and collected. (Ch.2)

Screening — the first, presumptive stage of toxicological analysis: a fast, broad, deliberately sensitive test (typically an immunoassay) that produces leads rather than identifications and must be confirmed before it counts as proof. (Ch.20)

Secondary scene — any other location connected to a crime that holds related evidence but is not the site of the principal act (e.g., a body-disposal site, a suspect's vehicle, a weapon-discard location, or the route between scenes). (Ch.2)

Secondary transfer — the arrival of DNA on an object because its source contacted something or someone else that then contacted the object, rather than the source contacting the object directly; the central interpretive hazard of touch/trace DNA. (Ch.8)

SEM-EDX (scanning electron microscopy with energy-dispersive X-ray analysis) — the combination of a scanning electron microscope, which images a particle's shape and surface at very high magnification using a focused electron beam, with an energy-dispersive X-ray detector, which determines the particle's elemental composition from the characteristic X-rays the beam excites; reveals both what a microscopic particle looks like and which elements it is made of. Elemental composition is class evidence, not individualization. (Ch.23)

Sequential unmasking — a context-management procedure in which the examiner first analyzes the evidence sample on its own and documents that interpretation in writing before being shown any reference sample or comparison material, after which information is revealed in a controlled order (most-biasing information last, and only when actually needed), with each conclusion recorded before the next layer of context is unmasked. (Ch.31)

Sequential vs. simultaneous (lineup presentation) — simultaneous presents all lineup members at once, inviting a relative "pick-the-closest" judgment; sequential presents them one at a time with a forced yes/no on each, pushing toward an absolute memory comparison. The presentation order matters less than the other safeguards. (Ch.32)

Serology — the forensic identification, characterization, and (historically) grouping of blood and other body fluids such as semen, saliva, and urine; modern serology focuses on whether a biological fluid is present and which one it is. (Ch.10)

Sex estimation — assessment of biological sex from the skeleton, most reliable from the adult pelvis and secondarily the skull; reliable mainly in mature adults, reported as a probabilistic, class-level estimate rather than a certainty, and distinct from a person's gender identity. (Ch.12)

Sexual-assault evidence kit — a standardized package of swabs, envelopes, slides, and documentation forms used by a trained examiner to collect, label, and preserve biological and trace evidence from the body and clothing of a sexual-assault patient for possible laboratory analysis; it collects and preserves evidence but does not, by itself, prove that a crime occurred. (Ch.37)

Signature — behavior that goes beyond what is functionally necessary to commit a crime, performed to satisfy a psychological or emotional need; theorized to be more stable than MO across an offender's crimes and therefore more useful for behavioral linkage. (Ch.28)

SNP (single-nucleotide polymorphism) — a position in the genome where individuals commonly differ by a single base; large panels of SNPs are the basis of genealogical relatedness matching. (Ch.8)

Soil comparison — the examination and comparison of the physical, mineralogical, chemical, and biological (including pollen) properties of a questioned soil against known and control samples from locations of interest; class evidence whose strength scales with the soil's distinctiveness and the adequacy of control sampling, capable of associating an object with an environment but not of fixing time or proving guilt. (Ch.24)

Spatter — blood dispersed through the air as droplets by an applied force; a physical description of dispersed drops, not a conclusion about what force or event produced them. (Ch.10)

Spectroscopy — the family of analytical methods that identify and characterize a substance by measuring how it absorbs, emits, or scatters electromagnetic radiation across a range of wavelengths; the resulting spectrum reflects the substance's molecular structure. (Ch.23)

Stature estimation — inference of living height from bone length (most reliably the femur and other long bones) using population- and sex-specific regression equations; reported as a range, not a single number. (Ch.12)

STR (short tandem repeat) — a short DNA sequence (typically 2–6 bases) repeated back-to-back a variable number of times at a fixed genomic location; the between-person variation that standard forensic typing exploits. (Ch.7)

Strangulation findings — the constellation of observed signs and reported symptoms a forensic examiner documents in a strangulation assessment (e.g., petechiae, voice change, difficulty swallowing, and reported loss of consciousness or incontinence); strangulation can be serious or lethal with little or no external neck injury, so a normal-appearing neck does not rule it out. (Ch.37)

Striations — the fine parallel lines scraped onto a fired bullet (and onto toolmarks generally) by the microscopic irregularities of the barrel's interior; the correspondence of striations between a questioned and a known bullet is the basis — and the contested basis — of a same-source firearms identification. (Ch.15)

Succession — the predictable sequence in which different insect (and other arthropod) species colonize and then depart from remains as the body changes state; read as a clock for longer postmortem intervals. (Ch.13)

T

Taphonomy — the study of everything that happens to remains between death and analysis (decomposition, weathering, scavenging, soil and water action, burial, and fire); both a reconstructive tool and a trap, because taphonomic damage can mimic or mask trauma. (Ch.12)

The CSI effect — The distortion of juror and public expectations by fictional portrayals of forensics, which simultaneously makes juries demand impossible certainty and over-trust weak forensic testimony. (Ch.1)

The Innocence Project — the legal organization founded in 1992 by Barry Scheck and Peter Neufeld (originally affiliated with the Cardozo School of Law) to exonerate the wrongly convicted through post-conviction DNA testing and to reform the causes of wrongful conviction. (Ch.6)

Therapeutic range — the band of blood concentrations at which a drug produces its intended effect with acceptable safety; a finding here is consistent with appropriate medical use, not poisoning. (Ch.20)

Tire impression — the recorded tread detail left by a vehicle's tire; class characteristics (tread design, width, dimensions, noise treatment) can yield a make/model and place a vehicle — not a driver — at a scene, while acquired characteristics (cuts, stone-holds, wear) can in principle narrow toward an individual tire. (Ch.16)

Toolmark — any impression, scratch, gouge, cut, or abrasion produced when a harder tool contacts a softer surface; analyzed as class evidence (the tool's general shape and size, from impressed marks) and, contestably, individual evidence (fine striations from a tool's working edge). (Ch.16)

Touch DNA — genetic material recovered from the skin cells a person sheds onto an object by handling it (also called contact DNA); names a sample type that is typically low in quantity. (Ch.8)

Toxic range — the band of concentrations above therapeutic at which harmful effects (impairment, incapacitation, organ stress) appear, without necessarily being fatal. (Ch.20)

Trace DNA — the broad umbrella term for any tiny, often invisible biological deposit (touch DNA included) from which a DNA profile might be recovered. (Ch.8)

Trace evidence — physical evidence found in small or microscopic quantities, transferred between people, objects, and environments by contact (hairs, fibers, glass fragments, paint chips, soil, gunshot residue, pollen, and the like); defined less by what it is than by how little of it there is and how it got there — the direct application of Locard's exchange principle. (Ch.19)

Transfer/persistence — transfer is the movement of material from one surface to another on contact (primary = direct; secondary = through an intermediate surface or person); persistence is how long the transferred material remains before it is shed, washed, or worn away; together they govern whether a trace is recoverable and how its presence may be interpreted. (Ch.19)

Transient evidence — evidence that is temporary by nature (odors, temperature, a wet vs. dry stain, a flame's color, a dying statement) and can be preserved only by immediate documentation rather than collection. (Ch.3)

Trauma-informed practice — an approach to interacting with people affected by violence that recognizes the widespread effects of psychological trauma, actively seeks to avoid re-traumatizing the person, and structures the encounter (pacing, setting, language, patient control) around that recognition — improving both patient welfare and the reliability of the resulting evidence and testimony. (Ch.37)

U

Ultimate-issue rule — the principle governing whether, and how far, a witness may offer an opinion on the ultimate issue the jury must decide (such as guilt or a required mental state); modern rules let an expert state an opinion that embraces an ultimate issue but still forbid usurping the jury by testifying to guilt. The line is between informing the jury's decision and making it. (Ch.30)

V

Validity spectrum — The range along which forensic methods fall according to the strength of the scientific foundation for their core claim, assessed against the 2009 NAS report and the 2016 PCAST report. (Ch.1)

Voir dire — the preliminary examination of a proposed expert witness, conducted before substantive testimony, to determine whether their qualifications, methods, and proposed opinions meet the legal standard for expert testimony; if survived, the court "qualifies" or "accepts" the witness as an expert in a stated field. (The same term also names the questioning of prospective jurors.) (Ch.30)

W

Weight of evidence — the overall strength with which the total assembled body of evidence supports a particular conclusion, expressed honestly on the book's scale (excludes → consistent with → strongly supports) and never inflated to the forbidden "proves." (Ch.39)

Whorl — a level 1 pattern containing at least one ridge that makes a complete circuit (a spiral, circle, or twinned loops). (Ch.14)

Wildlife forensics — the application of forensic science to crimes and legal questions involving wild animals and plants (poaching, illegal trade in protected species and their parts, conservation-law violations), most centrally through identifying the species — and sometimes the population, individual, or geographic origin — from biological evidence. (Ch.36)

Write blocker — a hardware or software device placed between an evidence drive and the examiner's computer that permits data to be read from the drive while physically preventing any write to it, ensuring the original is not altered during acquisition. (Ch.25)

Wrongful conviction — the conviction of a factually innocent person; distinct from a conviction reversed merely on legal or procedural grounds (where the convicted person may in fact be guilty). (Ch.6)

Y

Y-STR — STR typing restricted to the male-only Y chromosome; able to isolate a male contributor from a female-heavy mixture but shared along a paternal line, so it identifies a lineage rather than an individual. (Ch.8)