Despite what you see on all those crime shows, medical examiners don't actually know how long a corpse has been dead, reports LiveScience. Lacking a precise method to determine time of death, pathologists essentially make a good guess. But a new study focused on the necrobiome—the world of organisms involved in decomposition, including bacteria—could change the game for forensic scientists. "By knowing which microbes take over a dead body and how long it takes, forensic scientists might be able to use this technique to determine time of death or other aspects of a crime scene," one expert says in a statement. Writing in the journal PLOS ONE, researchers from CUNY say the current "crude" methods for examining a corpse involve a physical inspection for signs of decomposition and for insects present. "These techniques are notoriously unreliable," they explain, because they are skewed by temperature and weather conditions, among other factors.
Researchers placed 21 cadavers outdoors in a temperate forest to decompose naturally over several weeks, and then studied their necrobiomes by swabbing bacteria from ears and nostrils. They used the findings over time to build a statistical model that can map time of death to up to 55 "accumulated degree-days," or about two summer days. "When it comes to rates of decay, one day in summer time is like two weeks in winter time," lead author Nathan Lents tells LiveScience. A decomposing body undergoes "wild changes" over time and as the temperature changes, so "accumulated degree-days" offer a way to measure both time and temperature changes simultaneously. Although more research is needed, Lents thinks the team's model "will eventually become the standard method" for pinpointing the time of death in bodies that have been sitting out for a while. (Your microbiome may be keeping you healthy.)