The clock is essentially the succession of bacterial changes occurring postmortem as bodies go through the decay process, the university said in a release.
Researchers used mice for the latest study, but previous studies on the human microbiome -- the estimated 100 trillion or so microbes that live on a body -- indicate there is reason to believe similar microbial clocks tick away on human corpses, said Jessica Metcalf, a CU-Boulder postdoctoral researcher and lead author of the study.
"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. "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."
Using high-technology gene sequencing techniques on bacteria and microbial eukaryotic organisms such as fungi, nematodes and amoeba postmortem, researchers said they pinpointed the time of mouse death after a 48-day period to within about four days.
The results were more accurate after an analysis at 34 days, correctly estimating the time of death within about three days, Metcalf said.
The researchers tracked microbial changes on the heads, torsos, body cavities and associated grave soil of 40 mice at eight different time points during the 48-day study.
The stages after death include the "fresh" stage before decomposition, the "active decay" that includes bloating and subsequent body cavity rupture, and "advanced decay," said Chaminade University forensic scientist David Carter, a co-author on the study.
"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 faculty member 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."