Strands of Evidence

  • By Ari Daniel
  • Posted 10.11.12
  • NOVA scienceNOW

You are what you eat, and what you eat ends up in your hair. Scientists in the U.S. and Europe have used this basic idea—and some sophisticated isotopic analysis—to devise a sort of hair-based GPS tracking system. A single strand contains information on your whereabouts over the past few months, a fact that law enforcement agencies are now using to solve crimes.

Listen to the story.

Your hair may reveal more about you than you realize—including where you live and where you have been.

Lesley Chesson opens a cardboard box inside her office at IsoForensics, a Salt Lake City-based company that uses science to fight crime. She pulls out a bulging manila envelope.

"That one definitely has hair in it," she says with a chuckle.

A senior scientist at the company, Chesson reaches into the envelope and removes a mass of brunette hair. Her colleague, Luciano Valenzuela, looks over a list to see where it came from.

"It's hair from Shawnee, [Oklahoma]," he says.

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Lesley Chesson holds up one of nearly 2,000 human hair samples stored at the company IsoForensics. Enlarge Photo credit: Courtesy Ari Daniel / WGBH Educational Foundation

Another 2,000 envelopes and vials stored here also contain human hair, collected from across the United States and around the world. "Guatemala, Japan, Newfoundland, Thailand," says Valenzuela, rattling off some of the countries.

In fact, the scientists have hair from every continent, even Antarctica. They are using all this hair—from regular, everyday people—to perfect a technique to help solve murder cases.


Both Chesson and Valenzuela were mentored by a professor at the University of Utah, Jim Ehleringer.

Ehleringer was trained as a plant biologist, but about a decade ago, he became curious about animals and whether he could develop a new technique for addressing a question that wildlife biologists commonly ask: where do animals eat and drink, and does the location of their watering hole, say, change over time?

"I could find out by being in the field every single minute of the day," he says. "Or I can let nature do the recording for me."

Ehleringer realized that what an animal eats and drinks does get recorded—in its tissues.

Every chemical element comes in different forms, known as isotopes, with some slightly heavier than others. Take hydrogen and oxygen, the atoms that make up water, H2O. Their different isotopes are found in different concentrations depending on where the water comes from. And that mixture of heavy and light atoms gets laid down in the growing tissues of the animals that drink the water. These tissues include hair.

"The hair becomes a linear tape recorder," says Ehleringer. "So it tells us a little story about the history of what an animal was eating or drinking."

Our hair acts as a timeline—recording where each of us has been and when we were there.

Ehleringer suspected the same thing would apply to humans and our hair. So he and his colleagues collected hair from local barbershops across the U.S. to test a hypothesis. They wanted to determine if it was possible to tell where hair came from based on an analysis of the hydrogen and oxygen in the local water supply.

Thure Cerling, a geologist at the University of Utah and another collaborator on this project, says the vast majority of the water in our diet is local.

"People often say, 'Well, oh, I don't drink water. I drink Coke,'" he says. "[But] where was the Coke or the Pepsi bottled?" It's usually at a local bottling plant, using local water.

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Different isotope levels in tap water across the United States are depicted using different colors. Enlarge Photo credit: Courtesy IsoForensics, Inc. 2012


Sure enough, the scientists found that hair—and water—look different in different parts of the U.S. They can display that variation on a map with rainbow colors.

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In general, hair grows at a rate of 1 centimeter per month, as Lesley Chesson and Luciano Valenzuela demonstrate. Enlarge Photo credit: Courtesy Ari Daniel / WGBH Educational Foundation

"It looks like the temperature map that you see during the news that will show you where [it's] hot and where [it's] cold," says Luciano Valenzuela.

Red colors flare in Texas and Florida. The Midwest is yellow. And blue coats states like Montana, Wyoming, and Idaho.

With this information, it is possible to examine a single strand of hair, compare it to the map, and get a pretty good idea of where someone was when that hair grew. And by looking at how the isotopes change along the length of the hair, scientists can determine if someone has traveled.

In other words, our hair acts like a timeline—recording where each of us has been, and when we were there. It soon became clear that this tool could be valuable in solving crimes.

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Hair samples occupy countless vials, awaiting analysis. Enlarge Photo credit: Courtesy Ari Daniel / WGBH Educational Foundation


At about the same time that the Utah scientists were developing this technique, a team in the United Kingdom was working on the same approach.

Wolfram Meier-Augenstein, a chemist at the James Hutton Institute in Scotland, has examined the isotopic composition of hair and water in Europe and the Middle East, and he has used that information to help police in the U.K., United Arab Emirates, and elsewhere with about a dozen murder cases.

He is not at liberty to talk about most of those cases, but in one case he can discuss, a man was found dead in Wales several years ago. The man appeared to be Asian, but police did not know where he came from or when he entered the U.K.

The man's hair was almost six inches long. Meier-Augenstein explains that was long enough to determine where the man had lived in the year before he died.

"The person lived in the Ukraine for three months, moved then to Germany for six-and-a-half months, and then to the United Kingdom prior to his untimely death," he says.

The police knew of an organized crime gang that was shuttling illegal Vietnamese immigrants into Britain via Ukraine and Germany. The police suspected the murder victim had been smuggled into the U.K. by that gang.

By examining isotopes in hair, scientists can also learn other things about a person diet—including whether someone was vegetarian or vegan, preferred fish to chicken or beef, or had gone through an sustained period of starvation.

Once the clue from the hair analysis had confirmed that suspicion, the other bits of the puzzle came together. The police learned that the man was originally from Vietnam and had been killed in a dispute over marijuana.

"In any homicide investigation, knowing who the victim is, is critical—who they associate with, where they've been," says John House, head of the criminal investigative division at the Royal Newfoundland Constabulary, in Canada.

House has used this type of forensic analysis of hair and says it can offer a starting point for murder cases that would otherwise go cold fast. "Without that information, we're really at a standstill," he says.

By examining isotopes in hair, scientists can also learn other things about a person's diet—including whether someone was a vegetarian or vegan, preferred fish to chicken or beef, or had gone through a sustained period of starvation. All of these details might prove helpful in identifying a murder victim.


Back in Salt Lake City, Luciano Valenzuela pulverizes a hair sample in a machine that looks like a small version of a paint can shaker. This is one of the first steps the staff at IsoForensics uses to analyze hair isotopes.

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Human hair samples at IsoForensics Enlarge Photo credit: Courtesy Ari Daniel / WGBH Educational Foundation

The company gets requests from law enforcement agencies once or twice a month, and the demand is growing. Meanwhile, the scientists continue to refine the technique by gathering more hair from other parts of the world.

"Obviously, everywhere we go and every time we get a chance, we continue to collect samples," says Lesley Chesson.

She looks over at Valenzuela, who is from Argentina. "Luciano," she says, smiling, "maybe we should send you home for Christmas—send you on a collecting trip." They both laugh.

That chance will come soon enough. Valenzuela returns to Argentina next year to start his own lab. His goal is to create a detailed map of the invisible variations in hair and water across his own country.

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