One of the most important tasks for a forensic scientist investigating a death is to determine when the person died. Up to 48 hours postmortem, those investigators can use medical methods such as the stiffness or temperature of the body. Longer than that, and they have to turn to the beetles and flies that take up residence in cadavers, using their age and natural succession to estimate the time of death. After about a month, however, there is nothing left to eat and the insects jump ship, leaving investigators without a means of figuring out the age of the corpse.
Forensic biologist Ildikò Szelecz of the University of Neuchatel in Switzerland wondered whether microscopic soil-dwelling organisms could help date older corpses. After all, a body in their midst would presumably affect their ability to thrive. So she and her colleagues placed three dead pigs on the ground and measured their effects on the density of testate amoebas in the soil underneath the cadavers. Testate amoebas are a motley group of single-celled organisms that have shells of many shapes called tests. As it turns out, the 23 species that the team examined abhor corpses—not a single living amoeba could be found under the pig cadavers at 22 and 33 days after placement. “I was expecting a reaction but not that they all died after a certain time,” Szelecz says. The study results were published in Forensic Science International.
Only by day 64 did the amoebas start to rebound in the soil under the pig. But even after nearly a year, their populations had still not entirely returned to normal compared with controls. Decline and recovery of these microorganisms thus provide a potential way to measure the age of bodies that have languished outside for a considerable period. Just how long remains to be seen: a five-year study involving 13 pig cadavers is under way now.