Part II — Biological Evidence

This is the part where forensic science earns its reputation — and where the Cold Case turns over. Biological evidence includes the field's one rigorously validated method, DNA analysis, and it is no accident that the book treats DNA first and at length. Everything that follows is measured against it. But Part II is not a victory lap. The same chapters that celebrate DNA's quantified rigor also teach the statistics that make a "match" meaningful or dangerous, the contested business of reading bloodstains, and the hard-won lessons of pathology, anthropology, and entomology — the disciplines that read the body itself.

The arc moves outward from the molecule to the body to the scene around it. We begin with DNA and push it to its limits — touch samples, mixtures, degraded traces, and the genealogy that closed the Golden State Killer case — then confront the numbers that any DNA result lives or dies by. From there we widen the lens: blood and body fluids, the autopsy that establishes how a person died, the skeleton that testifies when soft tissue is gone, and the insects and plants that keep time. Somewhere in this part, the Cold Case's central assumption collapses.

  • Chapter 7 — DNA Analysis: How Genetic Evidence Revolutionized Criminal Investigation lays out the one method built on rigorous, quantified science — extraction to electropherogram to CODIS — and the random match probability that gives a match its weight.
  • Chapter 8 — Advanced DNA: Touch DNA, Degraded Samples, Mixtures, and Forensic Genealogy pushes DNA to its edges, where interpretation — and error — creep back in, and introduces investigative genetic genealogy.
  • Chapter 9 — Forensic DNA Statistics: Match Probabilities, Likelihood Ratios, Mixtures, and the Prosecutor's Fallacy confronts the truth that a "match" is a number, and a meaningless one unless interpreted correctly. This is the chapter that arms you against the prosecutor's fallacy for the rest of the book.
  • Chapter 10 — Blood and Body Fluids: Serology, Presumptive Testing, and Bloodstain Pattern Analysis separates the validated work of identifying body fluids from the far more contested attempt to reconstruct events from spatter.
  • Chapter 11 — Forensic Pathology: How the Body Tells Its Story After Death establishes cause and manner of death — and in the Cold Case, the autopsy overturns the entire premise.
  • Chapter 12 — Forensic Anthropology: Bones, Identity, and the Unidentified Dead reads identity and trauma from the skeleton when fire or decomposition has taken everything else.
  • Chapter 13 — Forensic Entomology and Botany: When Insects and Plants Solve Cases turns insects and pollen into clocks and witnesses that can estimate time of death and place a vehicle at a scene.

Part II advances all four themes, but two carry it. The first is, again, not all forensic methods are equally valid — but here the spectrum is shown from its strong end. DNA is what a validated forensic method looks like, and seeing it done right (Chapters 7–9) gives you the standard against which Part III's weaker methods will be found wanting; even within this part, Chapter 10 shows serology's rigor sitting next to bloodstain analysis's controversy. The second is forensic science excludes; it rarely proves: DNA's surest power is still the clean exclusion, and the chapter on statistics teaches you to state even a strong inclusion at its true strength — a number, against a stated alternative, never a certainty.

Chapters in This Part