National Geographic : 2016 Jul
38 national geographic • july 2016 in forensic science, and some critics question how useful it will be. The facial composites it produces are predictions from genetics, not pho- tographs. Many aspects of a person’s appearance are not encoded in DNA and thus can never be unearthed from it, like whether someone has a beard, or dyed hair. Nevertheless, Parabon, which calls its facial composite service Snapshot, has had more than 40 law enforcement organi- zations as customers. Human genome pioneer Craig Venter, as part of his new personalized health company called Human Longevity, is also investigating facial reconstruction from DNA, as are many academic labs. Meanwhile other high-tech forensic meth- ods are coming on the scene. CT scanners allow doctors to perform virtual autopsies, peering into bodies for signs of murder undetected by standard autopsies. Researchers are studying whether bacteria on corpses can provide a more accurate clock to gauge when death occurred. And they’re even investigating whether culprits might be identified not just by the DNA left at a crime scene but also by the microbial signature of the bacteria they leave behind. The forensic techniques we’re more familiar with from movies and television shows such as CSI have far longer histories. In 1910 Thomas Jennings became the first American convicted of murder based primarily on fingerprint evi- dence. He was accused of shooting one Clarence Hiller during a bungled burglary. The culprit had left his fingerprints behind on a freshly painted windowsill, and the testimony of four fingerprint experts was nearly the entire basis on which Jennings was found guilty and sen- tenced to death. In response to his appeal, a higher court pointed both to the long heritage of using fingerprints for identification—pharaohs employed thumbprints as signatures, they said—and to “the great success of the system in England, where it has been used since 1891 in thousands of cases without error.” The court did caution that because such evidence fell beyond the purview of the average person’s experience, it must be presented by experts who could ex- plain it to the jury. The verdict was upheld, and Jennings was hanged. By the late 20th century, there were numer- ous investigative techniques in the courtroom. FBI analysts gave testimony comparing hairs found at a crime scene with those from sus- pects. Hair-analysis experts note the shape of the microscopic scales that coat hairs, the thickness and coloration of the hair, and the organization of pigment granules in it, among other qualities. Bite-mark analysis, in which experts compare the pattern left by a bite on a victim to a suspect’s teeth, was widely adopt- ed in the early 1970s, including a 1974 court case that hinged on marks identified on a dead woman’s nose after she’d been exhumed. Other visual comparisons—between tire tracks, shoe prints, and patterns on bullet casings—also made their way from being clues used by law enforcement to identify suspects to becoming evidence presented in court to help prove guilt. In thousands of cases, judges tasked with de- ciding whether evidence is reliable have leaned on ample precedent to allow such forensic results to be admitted in court. Experts with years of experience at their craft have testified with assurance. But over the past decade or so, it’s become apparent that many forensic methodologies offer far less certitude than TV dramas suggest. And when forensic evidence is oversold in court, innocent people go to jail, or worse. Many forensic methods offer far less certitude than TV dramas would suggest. And when forensic evidence is oversold in court, innocent people go to jail, or worse. n Grant Your National Geographic Society membership helped fund DNA-phenotyping research.