Estimating time of death: a foray into forensics
Time of death (TOD) is an important indicating factor in forensic investigation. The oldest, and easiest, method of estimating TOD involves core body temperature (usually obtained with a liver probe, just like they show on CSI) and/or observed progression of rigor mortis.
The TOD estimation based on temperature is really kind of an iffy thing. The equations for this include many corrective factors to account for variables such as body weight (and fat content), average environmental temperature (which can be unreliable, as it may be subject to large variations over time), degree of exposure (e.g. clothes or other coverings on the body), air or water movement around the body, and substrate (pertains to conductive heat transfer through adjacent surfaces). This involves a lot of educated guesswork by the investigators. Henssge et al. recommended that additional methods of estimating TOD be employed where possible.
(Also, the body temperature is only really useful with relatively "fresh" bodies, because after a while the temperature comes to equilibrium with the environment, after which point the body temperature can't tell you much at all. Another major skewing factor can throw off the entire method when the body is moved from the site of death prior to the start of an investigation. Then, of course, there are cases where the fatal event, constituting the actual crime that the investigators want to solve, doesn't immediately precede death; this opens up a whole other can of worms.)
It is generally accepted that the "average" case of rigor mortis lasts 2-4 days post-mortem. It is also generally accepted that lower-than-"average" temperatures cause this time period to increase. Varetto et al. performed a study in which human cadavers were stored at a constant temperature of 4 degrees Celsius, representing average winter outdoor temperatures in temperate regions. They found that complete rigor lasted at least 10 days and up to 16 days, which is much longer than is usually indicated in forensic medical texts. Partial rigor was observed up to 27 days post-mortem, with complete "relaxation" seen on day 28. Based on these results, Varetto et al. concluded that at this temperature, it can be expected that complete rigor will persist 11-17 days post-mortem, with rigor disappearing altogether by day 28.
Henssge et al.: "Experiences with a compound method for estimating the time since death."
Varetto & Curto: "Long persistence of rigor mortis at constant low temperature."
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Labels: science
posted by the alygator @ 10:02 AM
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