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FORENSICS CAN BE used to prove guilt—or innocence. Studies of tobacco ash and “footsteps” enhanced the reputation of Sherlock Holmes in the late 19th century. For example, his Upon the Distinction Between the Ashes of Various Tobaccos is cited by chronicler Dr. John H. Watson in “The Boscombe Valley Mystery.” Recently, Science, the magazine of the American Association for the Advancement of Science, devoted a Special Section to forensics, with the subhead, “Evidence on trial.”
The articles include failures as well as successes of scientific techniques such as DNA and microbe evidence, voice analyses, even fingerprints. I offer here only one aspect addressed in Science: the use of human hair in capturing a culprit—or the wrong guy.
Despite a “hairsbreadth” and “winning by a hair,” the width of a human hair is anything but uniform. It can vary by more than threefold, from 30 to 100 μm, with perhaps an average of around 75 μm, about 0.003 in. These and other microscopic differences of hair have provided trial evidence.
In Washington, D.C., in 1978, a man in a stocking mask killed another man. Shortly afterward, a police dog discovered a stocking mask near the crime scene.
Informants fingered 17-year-old Santae Tribble as the assailant. What’s more, FBI analysis of hair on the stocking mask matched his hair “in all microscopic characteristics.” Prosecutors said there was only “one chance in ten million” that the hair belonged to anyone other than Tribble, and he was convicted.
Tribble served 23 years in prison, plus another five for parole violations, until being cleared of the original conviction on February 2016 because of enhanced analysis of the evidence. DNA identified the 13 hairs found on the stocking mask as coming from three different people, none of them Tribble, and from a dog. Tribble’s release after 28 years came with a court-ordered $13.2 million.
The Science Special Section contains “How Hair Can Reveal a History,” by Hanae Armitage and Nala Rogers. They say that forensic hair analyses of simply color, thickness and curvature have rightfully developed bad cred.
On the other hand, er, head, they also note that new techniques are improving matters. Most hairs found at a crime scene don’t contain enough DNA to support analysis. But keratin, the principal component of human hair, contains 21 amino acids, the ratios of which depend on human biochemistry.
Once hydrolyzed, the amino acids yield a profile that can be compared with a database to identify gender, age, body mass index and the region of geographic origin. The authors note, “The ratios of hydrogen and oxygen isotopes in drinking water vary from region to region and are captured in hair.” If the hair strand is of sufficient length, it can even provide a travel itinerary.
“Saltair Sally,” an unidentified woman found dead near Saltair, Utah, in 2000, is an example. By 2008, hair forensics had evolved, and samples of the woman’s hair were long enough to recognize isotope ratios differing within its length. The resulting clue that she repeatedly moved between the Salt Lake City area and the Pacific Northwest helped in her identification.
“Hardly elementary, my dear Watson.” ds
© Dennis Simanaitis, Dennis SimanaitisSays.com, 2016