Determination of “time of death” is a critical factor in any case involving the death of a victim. If a suspect cannot account for his/her whereabouts at “time of death”, he/she has a problem. If a suspect has a concrete, verifiable explanation for being somewhere other than at the scene at “time of death”, they cease to be a suspect.
But did you know that estimations of “time of death” are very imprecise, and subject to a wide range of physiological and environmental influences? If the “post mortem interval” (PMI) is less than ‘about’ 24 hours, the primary estimator is usually body core temperature. However, this will depend on ambient temperatures and humidities experienced by the body during the PMI, convection, sun exposure, the amount and type of clothing worn by the victim, and even how “fat” or “skinny” the victim is. Another indicator is “stomach contents”, but rates of digestion can very dramatically based upon a number of physiological factors. The onset and resolution of rigor mortis can vary by hours, as can the rates of post mortem lividity (settling of the blood).
I recently attended a presentation on the subject by Prof. Harrell Gill-King of the University of North Texas, who is a forensic anthropologist, and an expert in determining PMI. For a more complete understanding of the issues, his presentation is included here with his permission (just a caution – there are some “not nice” photographs included): PMI Presentation NADL
Here is an abbreviated version of Prof. Gill-King’s “Rules You Can Live With” for determination of “time of death”:
1) There is no single accurate marker of time of death, aside from a credible witness or a “time concurrence” feature.
2) Accuracy declines as the interval lengthens.
3) A range should always be given. A report of a ‘specific’ time of death is always suspect, and so is its author.