Establishing a precise time of death (the postmortem interval, or PMI) upon discovery of a corpse is notoriously challenging, however easy fictional medical examiners might make it seem. Some forensic scientists use the life cycle of blow flies, which seek out and lay eggs on corpses. But there’s a lot of variability between fly species and seasonal effects, so it would be helpful to develop new methods.
It turns out that studying the microbes that flourish in decomposing corpses can provide helpful clues. Forensic scientists have now identified some 20 microbes they believe constitute a kind of universal network driving the decomposition of dead animal flesh, according to a new paper published in the journal Nature Microbiology.
“One of the principal questions of any death investigation is ‘when did this person die?’” said Nancy La Vigne, director of the National Institute of Justice, which funded the research. “This continuing line of NIJ-funded research is showing promising results for predicting time of death of human remains, aiding in identification of the decedent, determining potential suspects, and confirmation or refutation of alibis.”
The work builds on nearly a decade's worth of prior research. For instance, in 2015, scientists were able to accurately estimate the time of death of mice and human corpses to within a two-to-four-day window, even after the bodies had decomposed for weeks. Earlier experiments had shown that, regardless of season, surroundings, and the species of the dead, communities of flesh-eating microbes seem to have a predictable timetable for when they dine on corpses. As Beth Mole reported for Ars at the time, "Those dining times relate to the stages of decomposition that a body undergoes—from fresh meat to bloated carcass, to rupturing and seeping nitrogen-rich fluids to actively decaying, then to an eventual dry state. Each stage attracts specific body-munching microbes, many with a taste for amino acids."