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ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

MELISSA BLOCK, HOST:

And I'm Melissa Block. Over the last few weeks, we've been exploring the role that microorganisms play in our lives, how microbes that live in and on our bodies affect our health. We've heard how doctors are trying to manipulate those microbes to treat us when we get sick.

Well, today, we're gonna hear about another way researchers are hoping to use those tiny organisms. As NPR's Rob Stein reports, they might help solve murders and other crimes.

ROB STEIN, BYLINE: Sibyl Bucheli got her first taste of how science can help solve crimes six years ago when a box arrived at her office in Huntsville, Texas.

SIBYL BUCHELI: And it was full of insects. It was just full of insects.

STEIN: The insects had been swept up at a crime scene. Police had found a badly decomposed body in a dilapidated house. Bucheli had just started working at Sam Houston State University as an entomologist and the cops figured she might be able to help. Bucheli immediately zeroed in on one of the bugs in the box.

BUCHELI: A moth.

STEIN: A common house moth, the type that eats your sweaters. As soon as she spotted it, she knew she was onto something.

BUCHELI: The moths make a cocoon, a portable shelter and it was putting pieces of the deceased's hair in its shelter.

STEIN: And even more exciting...

BUCHELI: The hair that was in the shelter had DNA in it.

STEIN: With DNA testing, the cops were able to identify the body and so began Bucheli's fascination with forensics.

BUCHELI: Good morning, Jordan.

STEIN: That fascination has brought Bucheli here, to the woods just outside Huntsville.

BUCHELI: This is the Southeast Texas Applied Forensic Science Facility. This is our center for anthropological research or forensic research.

STEIN: She leads us through a gate in a tall chain-link fence topped with razor wire down a dusty path into a small clearing. 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.

BUCHELI: There's actually four. One of them has become much more like soil.

STEIN: Four dead bodies in different stages of decomposition. One, just bones and gray dust, the others still covered in leathery skin, an odd pallet of dark brown, orange and yellow. Some still have hair, teeth.

BUCHELI: These are our research cadavers and so this is 011 and 009.

STEIN: They call this a body farm, one of the few places that scientists can leave bodies lying around in the open to study how they decompose.

BUCHELI: The one that you see we put out in late December, early January.

STEIN: Bucheli spent years studying how insects can pinpoint how long decomposed bodies have been dead. But that got Bucheli thinking, what about those other things we call bugs that aren't really bugs at all?

BUCHELI: If insects change through time, then so do bacteria. And if insects can be used, so can the bacteria.

STEIN: Our bodies are full of bacteria - on our skin, in our mouths, everywhere. Scientists think they could essentially become microscopic witnesses, witnesses that could tell police all sorts of things. We'll get to more about all that later. But for now, we'll focus on Bucheli's work, which she hopes will answer one of the most important questions in any murder investigation, when did the victim die?

BUCHELI: That's the ultimate question, how long. How long has that person been in the woods?

STEIN: By sampling bacteria from decomposing bodies, what she's found so far looks promising. The types of bacteria on a corpse seem to change in predictable ways over time. And as it turns out, other scientists have been finding the same thing.

BUCHELI: Do you guys want (unintelligible)?

UNIDENTIFIED WOMAN: Yeah, maybe, if you have them.

STEIN: Even though the hot sun is beating down, Jessica Metcalf is pulling on a white jumpsuit and plastic facemask. She works at the University of Colorado and has traveled to Huntsville with some colleagues today to team up with Bucheli's group.

JESSICA METCALF: So we're just gonna take some soil samples.

STEIN: Metcalf has already shown that bacteria can narrow down how long a mouse has been dead to within three days. She wants to prove it works with human bodies.

METCALF: You know, we're really pushing the envelope of microbial forensic science right now.

STEIN: To push that envelope, the researchers are placing three fresh bodies in the woods. A small tractor pulls up, carrying the first body inside a blue plastic body bag.

METCALF: You take him off this way.

STEIN: Three men lift the body off the tractor and place it on the ground.

UNIDENTIFIED MAN: Which way do you want the head?

STEIN: They unzip the body bag and carefully unwrap a white sheet swaddling the cadaver.

BUCHELI: We want to do this as respectfully as possible.

STEIN: It's a difficult moment. The older corpses are barely recognizable. They look like mummies. These bodies are people who just recently died and donated their bodies for scientific research. Bucheli is clearly moved. She pauses briefly for what she calls her thank-you moment.

BUCHELI: I am deeply appreciative of the people that make my research possible, all of them.

STEIN: The scientists mark each body's position with a metal post and then start several hours of intense work, meticulously gathering dozens of samples of bacteria.

BUCHELI: Do it. Let's do it.

STEIN: Carefully scrape the skin in the same spots on each body and methodically scoop up dirt in precise locations. They will come back day after day, month after month, to sample the exact same spots.

METCALF: What we're looking for is whether the microbial community changes in a clock-like manner. So we're looking for a microbial clock.

STEIN: A clock showing exactly how the species of bacteria on a decomposing body change as time passes. Microbes could also help police in many other ways, not just determining the time of death but helping figure out how someone died. The bacteria on a person who died naturally may look different than the bacteria on someone who was beaten to death.

And because different varieties of microbes are found in different places, they might show whether a body has been killed in one place and then dumped in another or when police are searching for unmarked graves.

METCALF: If you suspected that there's a body buried in a certain field, can we just swab little bits of soil and say, oh, you know, this particular area has microbial organisms that we usually find in soils that are associated with a decomposing corpse?

STEIN: And that's not all. Metcalf's boss, Rob Knight thinks microbes could provide a kind of microbial fingerprint while we're alive and help police solve all sorts of crimes.

ROB KNIGHT: What I have here are a bunch of swabs.

STEIN: Back in the office, he shows me how it works. He pulls out his laptop and demonstrates on the keyboard.

KNIGHT: You dip the Q-tip in the saline solution and you rub it very thoroughly on the individual key.

STEIN: The Q-tip quickly turns a greasy brown.

KNIGHT: So what's on there is a combination of finger grease, dust and bacteria.

STEIN: Like, how much bacteria?

KNIGHT: At least a million, maybe as many as a billion.

STEIN: Maybe as many as a billion?

KNIGHT: Right. And definitely enough to track it back down to an individual.

STEIN: Knight has been able to use this bacteria to match people to objects they've touched. So microbes might be able to do things like link a suspect to a murder weapon or the scene of the crime.

KNIGHT: There's a lot of cases where it's clear that the suspect touched something but you don't have a print you can use off it.

STEIN: All of this, Bucheli says, will hopefully answer the most important question for the families of victims. Who is responsible?

BUCHELI: You know, I'm somebody's mom. I'm somebody's sister. You know, you always think about, you know, who - who did this?

STEIN: Now, no one yet knows how much of this will turn out to work. And if it does, it's easily years away. But if it does work, it would raise lots of questions, questions about privacy, civil liberties and how much we want our microbes to reveal about ourselves. Rob Stein, NPR News.

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