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 鈥渨ave over a body鈥� to detect
how long the person has been dead. Arpad Vass of the Oak Ridge National
Laboratory, the lead investigator on the lab鈥檚 鈥渢ime since death鈥� programme,
says the first step is to create a look-up table of the chemicals made during a
body鈥檚 decomposition. You would then compare entries in the table with the
output of an electronic nose鈥攁 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.
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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 鈥渟ignatures鈥� 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.
鈥淚 have reservations about the aim of eliminating expert interpretations of
results,鈥� says Lee Goff, a forensic entomologist based in Hawaii, who has
estimated time of death for more than 200 corpses鈥攂ased 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.