Advances in DNA analysis, however, led to many exonerations of those who had been convicted using forensic examinations of hair samples.
In one notorious incident, the US Justice Department formally acknowledged in 2015 that FBI examiners overstated forensic matches in ways that favored prosecutors in more than 95 percent of 268 trials reviewed over two decades prior to the year 2000. Those mishandled cases included 32 defendants who had been sentenced to death.
According to the Innocence Project, a New York-based non-profit dedicated to exonerating the wrongfully-convicted, of the 349 people exonerated in the United States by DNA testing since 1989, 46 percent involved the misapplication of forensic science.
The new method, if adopted by investigators, could rehabilitate the field of hair analysis, bringing the approach back into the mainstream.
The approach is meant to compliment DNA testing, not replace it.
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Jackson’s method involves running an analysis of the hair’s chemical composition, focusing on amino acids found in keratin, the protein that is the primary material of human hair.
Unlike a DNA test, which reveals only a genetic profile, Jackson’s technique can also reveal recent behavior and lifestyle factors within a certain degree of probability.
"You could have genetically identical twins, and if one is obese and one is lean, we potentially could tell the difference between their hairs with our method," Jackson said.
What’s more, hair samples found at crime scenes often don’t carry enough DNA for a forensic analysis.
This new technique relies on liquid chromatography in conjunction with isotope ratio mass spectrometry to measure the ratio of isotopes — atoms with different numbers of neutrons — within 21 amino acids found in keratin.
To be sure, the method remains under development and, like earlier forensic hair analysis techniques requires more than a single strand of hair to be effective.
But Jackson told a press conference in San Francisco on Tuesday that it’s “a matter of time” before the sample size can be reduced to a single strand.
While the technique is still being refined, Jackson’s approach can now predict gender with 90 percent accuracy, and a subject’s body mass index with 80 percent accuracy.
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