New research revealed that microbes such as bacteria and fungi are the dependable “clock” that forensic experts may use to tell the time of death while a human cadaver is decomposing.
The team out of University of Colorado Boulder and University of California, San Diego found that these microbial communities tick in a clock-like succession following death – useful not just for estimating time of death but also determining the original location of corpses that had been moved or buried.
The study was published Dec. 10 in the journal Science.
Senior research associate and study lead author Jessica Metcalf highlighted their research’s great promise in forensic science.
"We view it as potential method that could be used with other lines of evidence by investigators attempting to solve suspicious crimes,” she said.
Metcalf added that these ubiquitous “decomposer” microbes, while rare in and on bodies and human surroundings before death, become abundant afterwards.
Each human contains up to about 100 trillion microbes, nearly 10 times as many cells in the body, that function from digestion to strengthening the immune system. The team then used gene sequencing to find those on cadavers and soils associated with them, considering both location and time quickly post-death.
The team involved 25 researchers working at the Southeast Texas Applied Forensic Science Facility of Sam Houston State University, a facility in Huntsville, Texas, that contains donated cadavers for forensic studies of bodies at varying decomposition phases.
Apart from analyzing human cadavers, the researchers also studied decomposing mice on desert, short-grass prairie, and high alpine forest soils. Microbial communities under the studied mice were similar across all three soils, akin to the predictable trail in soils lying beneath human cadavers.
In both human and mouse corpses, microbes on skin and soil offered accurate prediction of the time of death, with loosely two to four days of error estimated over 25 days. Further, decomposing bodies on soils significantly altered the soil microbes, allowing forensic experts to detect a decomposing body through the microbial community even though it has already been moved somewhere else.
Co-study lead author and UC San Diego professor Rob Knight said developments in gene sequencing technologies now allow researchers to find these patterns and associations when they couldn’t a few years earlier.
"This study extends the techniques we developed using the microbiome to predict disease while a person is alive, and shows the microbiome can also provide useful information after death,” he explained.
This microbiota technique is shown similar to blowflies, a currently used forensic tool attracted to vertebrate cadavers where they release eggs that develop into larvae in known time measures. However, the blowfly technique is restrictive due to cold seasons and accessibility of corpses.
The new study also pinpointed the value of vertebrate decomposition in land ecosystems. Decaying mammals contribute to the biological nutrient cycling, and microbial action on them shows how microbes gather and function to produce natural fertilizer.
Photo: Ariane Middel | Flickr
