A “microbial clock” could represent a reliable and extremely accurate way to determine time of death, a new study suggests. Researchers at the University of Colorado have discovered that by tracing the succession of postmortem bacterial changes, death can be pinpointed within four days after 48 days of decay. The new method may greatly benefit the work of law enforcement and forensic scientists.
According to post-doctoral researcher and first author Jessica Metcalf, current forensic inquiry relies on an inadequate analytic toolkit. Corpse temperature, text message, grave soil analyses, and insect infestation can only yield rough estimates. In addition, their accuracy tends to decrease exponentially as postmortem decay progresses.
“While establishing time of death is a crucial piece of information for investigators in cases that involve bodies, existing techniques are not always reliable,” Metcalf said in a press release. “Our results provide a detailed understanding of the bacterial changes that occur as mouse corpses decompose, and we believe this method has the potential to be a complementary forensic tool for estimating time of death.”
In an experiment, the researchers used advanced gene sequencing technology to assess bacteria and microbial eukaryotic organisms in deceased mice. Intriguingly, the postmortem changes in the sampled fungi, nematodes, and amoeba exhibited a surprising degree of consistency across all test subjects. The findings allowed the team to determine the time of death within three to four days after periods ranging from 34 to 48 days.
“At each time point that we sampled, we saw similar microbiome patterns on the individual mice and similar biochemical changes in the grave soil,” said Laura Parfrey, a microbial and eukaryotic expert at the University of British Columbia. “And although there were dramatic changes in the abundance and distribution of bacteria over the course of the study, we saw a surprising amount of consistency between individual mice microbes between the time points – something we were hoping for.”
A more reliable forensic process stands to benefit every aspect of crime investigation. For coroner technicians, an accurate time of death will undoubtedly facilitate further analysis. Similarly, the exact date of a murder will allow investigators to narrow their search.
“There is no single forensic tool that is useful in all scenarios, as all have some degree of uncertainty,” said Metcalf. “But given our results and our experience with microbiomes, there is reason to believe we can get past some of this uncertainty and look toward this technique as a complementary method to better estimate time of death in humans.”