Post-mortem interval is elapsed time since death; an estimated interval is not the same as an exact calendar time. Assess several suitable observations with their conditions and uncertainty.
Temperature models, rigor, lividity, chemistry and entomology have different assumptions. Agreement should be evaluated critically rather than mechanically intersecting dependent or invalid intervals.
By the end of this topic you will be able to:
- Distinguish discovery, examination, last-known-alive time and PMI.
- Explain assumptions of temperature, chemical and entomological approaches.
- Report intervals and convert them to calendar time correctly.
- Post-mortem interval (PMI)
- Elapsed time from death to the stated observation or examination.
- Algor mortis
- Temperature change whose interpretation depends on environmental and body history.
- Rigor mortis
- Post-mortem muscular change with condition-dependent development and resolution.
- Livor mortis
- Dependent blood settling with variable appearance and fixation; assess context.
- Vitreous humour potassium
- A chemical observation requiring a validated model and suitable sampling.
- Henssge nomogram
- A specific model tool, not every cooling chart; use its actual conditions and correction guidance.
Time of Death and Postmortem Interval: Key Differences
Separate the time of examination, last-known-alive information, discovery time and the estimated interval. Identify what each source actually establishes.
A last-known-alive time is evidence about a person being alive at an earlier point; discovery establishes when a body was found. Neither automatically supplies the moment of death. Convert any estimated elapsed interval to calendar time only after stating the examination reference time.
Algor Mortis and the Henssge Nomogram
Use temperature models within their applicable conditions and with the required measurements and correction guidance. Record environmental changes and sources of uncertainty.
A temperature model needs suitable body temperature, environmental information and other required inputs. Changing surroundings, altered clothing, immersion or heating can invalidate a simple constant-condition interpretation. The reported interval must retain the applicable model limitations.
Rigor, Livor, Gastric Contents and Vitreous Chemistry
Rigor and lividity vary; gastric contents are not a universal meal-to-death clock. Vitreous chemistry requires method- and population-appropriate interpretation, not an unqualified linear formula.
Decomposition Stages and Forensic Entomology
Decomposition and insect evidence require environmental, species and access information. Insect development may address a minimum colonisation interval rather than the entire time since death.
Entomological interpretation starts with identification, developmental stage, collection history and temperature exposure. Access delays and later movement can separate insect colonisation from death. Specialist analysis may therefore estimate a minimum period of insect activity rather than the full elapsed time since death.
Environmental Effects on PMI Estimates
Record actual exposure and changing environments. Country or season labels cannot replace temperature history and other case measurements.
Reporting PMI Ranges, Assumptions and Uncertainty
Report a supported range, assumptions and factors widening uncertainty. Do not turn a model output into an exact moment or select the narrowest interval without justification.
Check Your Understanding
Sources
- 1.Death Investigation: A Guide for the Scene Investigator (2024) · National Institute of Justice
- 2.Autopsy guidelines series · Royal College of Pathologists