A corpse's characteristic chemical cocktail could reveal the time of death
HOW do homicide detectives know how long a person has been dead? In the first 12 to 24 hours after death, visible changes in the body give an accurate enough estimate. But when corpses are days or weeks old it becomes more difficult because the complex chemistry of decay takes over and no one understands very much about it.
But now chemists, anthropologists and other scientists in Tennessee are working on a project to develop a device they could "wave over a body" to detect how long the person has been dead. Arpad Vass of the Oak Ridge National Laboratory, the lead investigator on the lab's "time since death" programme, says the first step is to create a look-up table of the chemicals made during a body's decomposition. You would then compare entries in the table with the output of an electronic nose-a device that detects and identifies vapours.
A body passes through three stages after death, says Vass: enzymatic liquefaction of cells (autolysis), bacterial decomposition of tissue (putrefaction) and then skeletonisation. These processes occur in the hours and days after death, at rates dependent upon the environmental conditions. Volatile gases are released, and organs liquefy and complex fats and proteins are broken down, but so far no one has quantified this process.
In an attempt to shed some light, Jennifer Love, a graduate assistant at the University of Tennessee, is spending successive nights in a morgue, taking vapour samples near corpses and samples of tissue from several organs, while noting temperature and humidity conditions.
Love says the Oak Ridge team is using mass spectroscopy, gas chromatography and electronic noses for odour analysis. The aim is to discover which absolute quantities of individual chemicals, ratios of related compounds or multi-component chemical profiles will correlate with different periods of time since death.
Vass has previously analysed the fatty acid content of the soil beneath corpses, and believes that such "signatures" let him estimate time since death with an accuracy of two days either way for every 30 days of decomposition. Eventually, in addition to a device that detectives would wave over a body, Vass would like to identify the chemicals that police dogs use to find corpses, so e-noses can do the job.
"I have reservations about the aim of eliminating expert interpretations of results," says Lee Goff, a forensic entomologist based in Hawaii, who has estimated time of death for more than 200 corpses-based on the stage in the life cycle of insects that quickly populate a body. Goff says that the many variables involved, such as body size and environment, will mean that a forensics expert will always be needed to evaluate the evidence.
Author: Jonathan Beard, New York
New Scientist issue: 17th June 2000
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