Scientists proved they can identify criminals using hair left at the scene of a crime

Identifying feature.
Identifying feature.
Image: Reuters/Juan Medina
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Forensic toxicology, the scientific investigation that teases out cause of death, is nothing like it is in the television shows. In reality, it takes weeks to months, rather than days, to identify perpetrators or victims.

But forensic scientists are hard at work seeking new ways to move that timeline up. In a paper published on Sept. 7, a team led by researchers at the Lawrence Livermore National Laboratory in California demonstrated that they are able to identify individuals by unique proteins found in hair.

At present DNA is the highest bar for identification in forensics. Though we all have fairly similar genes in a broad sense, what makes us different from our 7 billion neighbors is the distinct combination of variations of these genes, and how these combinations show up as physical traits. Which means if your DNA is found somewhere, you were almost certainly there.

The trouble for forensic toxicologists is that DNA breaks down pretty easily once it’s not in our living cells. “When the DNA molecule degrades from light, heat exposure or other environmental conditions, it becomes useless for identification,” Brad Hart, a chemist at Livermore’s forensic science division and co-author of the paper, said in a press release.

Hair, on the other hand, is quite durable. And although hair doesn’t contain DNA, it does hold some of the proteins that DNA codes for. “If there is a mutation in the DNA, it may show up in the protein itself,” says Deon Anex, a chemist at Livermore and co-author of the paper. “We’re basically exploiting the link between the protein back to DNA, which allows us to use a lot of the rules that apply to DNA.” In other words, your hair might be as unique as your genetic makeup. 

Here’s how it works: Hair is made of proteins, which are big molecules made out of smaller ones called amino acids. Proteins need to be structured in a certain way in order to function, but sometimes some amino acids can be traded for similar ones without any detrimental effect. You can think of the amino acids as different colored LEGOs: In most cases, swapping out a red brick for a blue one of the same shape won’t change the overall structural integrity of your final product.

The Livermore team found that if they could find these minor amino acid switches in a given protein, they could also trace those changes back to a single mutation in the DNA. Taken as a whole, the combination of these benign variations in protein structures in a strand of hair can provide the ability to identify individuals, just like DNA.

In the paper, the researchers analyzed hair from 66 men and women of European descent, five African Americans, five Kenyans, and even six sets of remains from the 1700 and 1800s. They found 185 distinct patterns of amino acids, called markers. They expect to find close to 1,000 markers as they continue their research, to make identification even more precise.

At the moment, says Anex, they require a sizable lock of hair to perform the chemical analysis needed to identify someone, but that they’re working to develop the technology to the point where could do it with a single strand. He estimates that it will be five to 10 years before hair will be able to identify single individuals like DNA can in a court of law. But, he expects that the technique will be useful for narrowing down suspects in a lineup more immediately.