When Did The Victim Die? The Microbes Know : Shots - Health News When bodies decompose, the types of bacteria on and around the body change in predictable ways. These patterns can be used to estimate time of death, a crucial clue in solving murders.
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Tiny Witnesses: Microbes Can Tell When A Murder Victim Died

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Tiny Witnesses: Microbes Can Tell When A Murder Victim Died

Tiny Witnesses: Microbes Can Tell When A Murder Victim Died

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AUDIE CORNISH, HOST:

Forensic investigators look at all kinds of factors when trying to estimate exactly when a victim has died. For example, the rate of body decomposition, how much carbon and nitrogen has leaked into nearby soil. But what about bacteria? How could understanding those microorganisms help police in a murder investigation? That's the question that NPR's Rob Stein started to explore two years ago when he visited an unusual research laboratory in Texas known as a body farm.

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ROB STEIN, BYLINE: It's a strange scene. For a moment, you don't even notice, scattered among the towering pine trees, the wild grass and weeds are bodies.

CORNISH: The farm is a place where forensic scientists study how bodies decompose. Next, Rob reports the results of that research, now published in the journal Science.

STEIN: This story feels like it could come right out of an episode of "Law & Order."

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STEIN: When the cops find a murder victim's body rotting in the woods, one key question is...

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JESSICA METCALF: When did the victim die?

STEIN: Jessica Metcalf's a forensic researcher at the University of Colorado. She says right now, medical examiners can only guesstimate based on things like how stiff the corpse is and what bugs are on it, but that doesn't always work.

METCALF: Every tool that a criminal investigator has is not perfect. That means that people can get away with murder.

STEIN: Because the time of death is crucial for all sorts of things, like knocking down a suspect's alibi.

METCALF: When a criminal investigator, say, is trying to solve a suspicious death and they want to know if particular people may have been involved, they need to know a timeframe.

STEIN: So Metcalf's team decided to see if the microbes that live all over our bodies might help. They placed two bodies in a field at the lab in Texas in the winter and again in the spring and came back over and over again for weeks to sample the bacteria, yeast and other organisms that were helping the corpses decompose.

METCALF: If microbial communities decompose carcasses in a very predictable way, then we can use this as a tool to help estimate that time since death - that succession of microbes becomes like a microbial clock.

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STEIN: And that's exactly what they found. They could narrow down the time of death to within a couple of days, no matter what the season.

METCALF: It worked very well. You have very predictable microbes showing up at very predictable times. What we're showing is that it's very clock-like.

STEIN: Which makes it a very powerful tool for forensic science.

METCALF: In a sense, your microbes are like witnesses to your death. As you decompose, they can help investigators solve your murder.

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STEIN: And other researchers agree.

JEFFREY TOMBERLIN: Oh, it's amazing.

STEIN: Jeffrey Tomberlin is a forensic researcher at Texas A&M University. He says investigators may be able to use microbes for a lot more than just determining when someone died. They could analyze the microbes in soil to find unmarked graves. And it turns out, people tend to pick up the unique kinds of microbes that live in different places.

TOMBERLIN: We might be able to apply that information to determine where a person died and what they were doing before they died. And these are very critical questions in any forensic investigation.

STEIN: Researchers have already shown that people leave traces of their microbes behind when they touch things, so they could be used like fingerprints to determine who touched the murder weapon.

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STEIN: And that's not all - Tomberlin thinks microbes could be used to trace the movements of suspected terrorists.

TOMBERLIN: So if you're curious if a person is moving between borders - say, Pakistan and Afghanistan - could you look at their microbial community? That may be a possibility.

STEIN: But, he says, this is all still really early. It'll take a lot more research to know for sure when investigators can start to use our microbes as our witnesses. Rob Stein, NPR News.

(SOUNDBITE OF MIKE POST SONG, "LAW & ORDER THEME SONG")

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