Chapter 4 Exercises: The Forensic Laboratory

These exercises run from recall to applied reasoning to ethics. Items marked with a dagger (†) have worked solutions in the answers appendix; do not look until you have tried them. Work in your own words — the point is to reason like a lab analyst and an attorney, not to recite definitions.

A. Recall and definitions

  1. In one sentence each, distinguish a crime laboratory's section from the laboratory as a whole. Why is the lab better described as a "federation of labs"?

  2. † Define accreditation. State precisely what it certifies and one thing it does not certify.

  3. What does ISO/IEC 17025 specify, and to whom does it apply? Name one U.S. body that grants accreditation to it.

  4. Write a one-sentence definition of quality assurance and a one-sentence definition of quality control. Which of the two does running a negative control belong to?

  5. † Define proficiency testing. What is the difference between a declared and a blind proficiency test, and why does the difference matter?

  6. Define method validation. State the difference between developmental and internal validation.

  7. List four properties a validation study measures (e.g., accuracy). Briefly say what each one means.

  8. Define contamination and list three distinct routes by which it can enter a result.

  9. What is a staff elimination database, and what problem does it solve?

  10. Name the two reviews that occur before a lab report is issued (per §4.1), and say what each one checks.

B. Comprehension and short application

  1. † A juror hears "this evidence was analyzed by an accredited laboratory" and concludes "so the result must be correct." Identify the reasoning error and correct it.

  2. Explain, in plain terms a juror could follow, why QA is the system and QC is the sample. Give one concrete example of each.

  3. A drug chemist's negative control unexpectedly develops color during a batch run. What should happen to the results in that batch, and why? What is the temptation under backlog pressure, and where does giving in to it lead?

  4. Why does the backlog matter for justice, not just logistics? Give one way it can harm an innocent person and one way it can harm public safety.

  5. † Explain why high sensitivity is both DNA's greatest strength and a contamination liability. Tie your answer to a specific control from §4.5.

  6. A lab adopts a new instrument and begins using it on real cases the following week, citing the manufacturer's published validation data. What essential step may have been skipped, and why is the manufacturer's data not sufficient?

  7. Distinguish a positive control, a negative control, and a reagent blank. For each, state what result should occur and what it means if that result does not occur.

  8. Explain the claim "a blank that flags contamination is a success of the quality system." When is contamination actually a problem?

C. Evidence interpretation and "spot the overstatement"

  1. † An analyst testifies: "Our lab is accredited, so you can be confident this result is reliable." Rewrite this as an honest statement that does not overstate what accreditation establishes.

  2. A report concludes that a method is reliable because the lab "passes all its proficiency tests." Identify two limitations of proficiency testing that this conclusion ignores (§4.3).

  3. Examine the claim: "The method is validated by the company that makes the kit, so our lab does not need to do anything further before using it." What is wrong with this, in the vocabulary of §4.4?

  4. A defense attorney argues that because a single analyst at a lab was found to have faked results, every case that analyst touched should be reviewed — even cases where no fraud is specifically proven. Is this reasoning sound? Defend your answer using §4.6.

  5. † An examiner says under oath: "Contamination is impossible in our laboratory." Critique this statement. What is the honest version of what a well-run lab can claim about contamination?

  6. Spot the conflation: a commentator says the Dookhan scandal and the Cameron Todd Willingham arson case (Chapter 22) are "the same problem — bad forensic science." Using the distinction drawn in §4.6's Junk-Science Alert, explain why they are different kinds of failure and require different fixes.

D. Reasoning and synthesis

  1. Construct a single piece of evidence (you invent it) and trace it through the six workflow stages of §4.1, naming one thing that could go wrong at each stage.

  2. † The chapter says every laboratory safeguard is "necessary and insufficient." Choose three safeguards (e.g., accreditation, controls, proficiency testing) and explain, for each, the gap between what it does and what it cannot guarantee.

  3. The independence problem (§4.7) is described as Theme 3 "scaled up from the individual to the institution." Explain what that means, and name the individual-level fix (Chapter 31) and the institutional-level fix (Chapter 38) the book later proposes.

  4. Suppose a jurisdiction wanted to make dry-labbing (reporting tests never run) much harder. Propose two specific controls from this chapter that would catch it, and explain how each would work.

  5. Connect this chapter to Chapter 1: the validity spectrum says a method's position is a "ceiling on reliability, not a guarantee." Explain how the lab quality systems in this chapter determine whether a method reaches its ceiling, using DNA as your example.

  6. † Connect this chapter to Chapter 2 (chain of custody) and Chapter 3 (Locard, evidence integrity): a single item is split between a county lab and a state lab. List the new risks this split introduces, and say which chapter's controls address each.

E. Ethics and judgment

  1. You are an analyst under intense backlog pressure. A detective hands you a sample with a note: "This is from our guy — just need you to confirm it's his blood for the arraignment tomorrow." Identify every problem with this situation from the chapter, and state what you should and should not do.

  2. † An analyst discovers that a respected senior colleague has been signing off on technical reviews without actually reviewing the work, to save time. The colleague says "I trust their results; it's a formality." What quality principle is being violated, what is the risk, and what is the analyst's obligation?

  3. A lab director is offered a chance to enroll the lab in a blind proficiency program but declines because "it might make us look bad if an analyst fails a hidden test, and our declared-test pass rate is already excellent." Evaluate this decision against the purpose of proficiency testing.

  4. You are asked to testify that your lab is "the best in the state" because it has the highest case-clearance numbers. Why should this make you uneasy, given the chapter's account of production pressure?

  5. An analyst is impaired on the job (compare the Farak case) but their declared-test performance remains passing. What does this reveal about the limits of declared proficiency testing as a safeguard against analyst misconduct?

F. Cold-case extension

  1. † (Cold case.) The Mill Creek evidence is split between the under-resourced Carrow County lab and the state crime laboratory, and the case is triaged low because the death was classified as a probable accidental fire. (a) Explain how the initial accidental-fire assumption (Chapter 1) has a second-order consequence for the evidence through the lab's triage system. (b) Name two specific risks the county-to-state split introduces, and the control from this chapter that addresses each.

  2. (Cold case.) A technician at the county lab examined the gas can and a separately packaged tool on the same uncleaned bench, without changing gloves, before a supervisor intervened. (a) Which contamination route from §4.5 is this? (b) The chapter says an extraction blank later came up clean. Explain precisely what that clean blank does and does not prove about the gas-can result.

  3. (Cold case.) An opposing expert will later cross-examine on lab handling. Draft three specific questions they might ask about the Mill Creek evidence's journey through the two labs, based only on this chapter, and explain what each question is probing for.

  4. (Cold case.) The "honest status after this chapter" is "Process framed; nothing concluded." Explain to a skeptical reader why it is correct — and important — that after an entire chapter on the lab, no person has been included or excluded and the accidental-fire assumption still stands.

  5. (Cold case, synthesis.) Imagine the cold case were worked by an independent laboratory with full blind verification and context management, instead of a small lab inside the local sheriff's structure. Name two specific points in the case so far where that difference might have produced a "cleaner" record, and tie each to the independence problem of §4.7.