Postmortem Interval Estimation
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Direct answer
The postmortem interval, or time since death, is estimated by combining postmortem cooling, rigor mortis, livor mortis, decomposition, stomach contents and environmental findings — never from a single sign. After death the body cools at an average of roughly half to one degree Celsius per hour, faster in the first hours, and this cooling corrected for body weight and ambient conditions on the Henssge nomogram is the most useful early indicator. The honest answer is always a range with stated assumptions, because clothing, air movement, humidity and body build modify every sign.
What you must remember
- Algor mortis: cooling follows a sigmoid curve — a brief initial plateau, then a near-linear fall, then a tail near ambient temperature; an average fall of about 0.5 to 1 degree Celsius per hour is commonly cited.
- Recording: rectal or intrahepatic temperature with a probe at a standard depth, plus the environmental temperature; the Henssge nomogram corrects for body weight and gives a confidence range.
- Crude guides: the body feels cold over exposed areas by about one to two hours and cold all over with rigor by four to six hours — palpation is no substitute for measurement.
- Rigor and livor: rigor onset one to two hours, generalised by twelve, off by twenty-four to thirty-six; livor onset half an hour to two hours, fixed by eight to twelve.
- Stomach contents: a light meal empties in about two hours, a heavy one in three to five; recognisable undigested food suggests death within about two to three hours of eating, modified by food type and stress.
- Vitreous potassium: rises slowly and roughly linearly after death, a useful laboratory adjunct but still an estimate.
- Later intervals: decomposition — greenish discolouration of the right iliac fossa within twelve to eighteen hours in warm weather, then gas and bloating — extends estimation into days, helped by insect succession.
Common confusion
Students quote a flat cooling rate of exactly one degree per hour, forgetting the plateau and the corrections, and may mistake a cold environment for a long interval. The second error is giving a single confident time — the expected answer is a range plus the modifying factors: clothing, obesity, air currents, sepsis, fever before death and position.
Exam-focused takeaway
Examiners ask the average cooling rate and the shape of the curve, the site of temperature recording, the basis of the Henssge nomogram, and the combined timetable of rigor, livor and decomposition. MCQs test the order of the early signs and the digestion timetable. In viva, answer with the combined-signs method, quote ranges, and volunteer the factors that shorten or lengthen each estimate.
Frequently asked questions
How fast does a body cool after death?
On average about 0.5 to 1 degree Celsius per hour, with a short initial plateau and a faster fall early, slowing as the body nears ambient temperature.
Which method best estimates the early interval?
Body cooling measured with a probe and interpreted on the Henssge nomogram, corrected for body weight and environment, combined with rigor and lividity.
What is algor mortis?
The postmortem cooling of the body as heat production ceases and heat is lost by conduction, convection, radiation and evaporation until ambient temperature is reached.
How do stomach contents help estimate time of death?
Light meals leave the stomach in about two hours, heavy ones in three to five; recognisable undigested food suggests death shortly after a meal.
Why must the answer be a range and not an exact time?
Because clothing, environment, body build, fever, sepsis and prior activity modify every postmortem change, only an approximate interval can be defended.
What helps estimate the interval in a decomposed body?
The pattern of decomposition, insect colonisation stages, adipocere or mummification, and scene findings such as dates on newspapers.