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San Diego Researchers Identify Possible Tool For Forensic Science

UC San Diego professor Rob Knight is pictured in this undated photo.
UC San Diego
UC San Diego professor Rob Knight is pictured in this undated photo.

Researchers at the UC San Diego School of Medicine announced Thursday that microbes can be used to provide a relatively accurate estimate of the time of death in decomposing human bodies.

The method could also be used to determine the original location of bodies that were moved and help locate buried corpses, according to a study published in Thursday's online edition of Science.

"We feel there is great promise that our findings could be used by forensic scientists," said Jessica Metcalf, staff research associate at UCSD and the University of Colorado-Boulder. "We view it as a potential method that could be used with other lines of evidence by investigators attempting to solve suspicious crimes."

Establishing a time of death is frequently a critical component in determining a defendant's guilt or innocence in a murder case.

Currently, investigators determine the time of death by studying blowflies, which lay eggs that develop as larvae in known time increments. The actions of blowflies, however, can be affected by weather conditions.

The human body harbors up to an estimated 100 trillion microbes — as many as 10 times the number of human cells in the body — that perform functions ranging from food digestion to strengthening the immune system.

The research team led by Metcalf and UCSD professor Rob Knight used a gene-sequencing technique to chart microbes present on cadavers and associated soils immediately following death.

"Advances in genetic sequencing technologies now allow us to find patterns in large, diverse populations of microorganisms, see how they associate with specific individuals, and understand how they change over time — in a way we couldn't just a few years ago," said Knight, who leads the UCSD Microbiome and Microbial Sciences Initiative.

The study developed its data using the Southeast Texas Applied Forensic Science Facility, a 26-acre outdoor human decomposition research lab at Sam Houston State University.

The facility, the largest of its kind in the world, uses donated cadavers that allow students, law enforcement officials and scientists to study bodies in various decomposition stages, aiding them in forensic science situations.

Knight said the microbial technique provided a time of death accurate to within two to four days, 24 days after a death occurred. That's about as accurate as the current method, and the microbes aren't impacted by variables like temperature, as blowflies are, according to the scientists.

The researchers also found that soil microbial communities are substantially modified by decomposing bodies. That means even if a body is moved, the original location can be detected.

Researchers from the Baylor College of Medicine, Chaminade University, Southwest Biological Science Center and University of Chicago participated in the study, which was funded by the National Institute of Justice's Office of Justice Programs, National Institutes of Health and the Templeton Foundation.