National Geographic : 2016 Jul
44 national geographic • july 2016 conclusions about the same fingerprint if they were told the print had come from a suspect who had confessed to the crime or was in cus- tody. In the case of Brandon Mayfield, a federal report revealed that the analysts had convinced themselves of similarities that didn’t exist. In 2009 the National Academy of Sciences released a blistering report calling into question the scientific validity of the analysis of finger- prints, bite marks, blood spatters, clothing fiber, handwriting, bullet markings, and many other mainstays of forensic investigation. It conclud- ed that with one exception, no forensic method could be relied on with a high degree of cer- tainty to “demonstrate a connection between evidence and a specific individual or source.” Not coincidentally, the one forensic meth- odology that passed scrutiny in the NAS report was developed not by law enforcement to aid the investigation of crimes but by a scientist working in an academic laboratory. In 1984 British geneticist Alec Jeffreys stumbled upon a surprising truth: He could tell people in his experiment apart solely by patterns in each per- son’s minced-up DNA, the genetic code we all inherit from our parents. Jeffreys’s discovery formed the basis of the first generation of DNA tests. Three years later Jeffreys’s lab processed DNA from a 17-year-old suspect in the rape and murder of two teenage girls in central England, and saw that it did not match DNA from semen found in the victims. Thus the first use of DNA in a criminal case led not to a conviction but to an exoneration. (The true killer later confessed, after he tried to elude DNA screening of a group of men in the area.) Soon other, more sensitive tests were in use, and by 1997 the FBI was employing one that looked at 13 places on the genome where stut- ters in the DNA code cropped up. The odds of any two unrelated people having the same 13 patterns were one in at least hundreds of bil- lions. It was these patterns that wound up form- ing the basis of the FBI’s CODIS database. By the 1990s, DNA profiling was being widely used in court cases around the world—in the Unit- ed States, most famously in the murder trial of O. J. Simpson. DNA evidence is hardly incontrovertible. Its value can be compromised by contamination from extraneous DNA anywhere along the chain from the crime scene to the laboratory where the sample is sequenced. A robust signal from semen, saliva, or tissue can narrow the proba- bility of a false match to virtually zero, but trace amounts of DNA left on an object handled by a suspect can yield much less accurate results. And a DNA sequence in a lab is only as good as the training of the person conducting the analy- sis. In April 2015 DNA analysis in the D.C. crime lab was suspended for 10 months and more than a hundred of its cases were reviewed, after an accreditation board found that analysts there were “not competent” and were using “inade- quate procedures.” It’s been seven years since the National Academy of Sciences report called for a com- plete overhaul of forensic science. Some of its recommendations—to create a National Insti- tute of Forensic Sciences, for example—are un- likely to come to pass for financial reasons, say government sources. Others, like an increase in research to establish how reliable fingerprints, bite marks, and other patterns really are at iden- tifying individuals, are under way. In the first five years after the NAS report, the National In- stitute of Justice spent $100 million on projects that have resulted in more than 600 scientific studies and reports. But the going is slow. “There are the rudiments of some important, Not coincidentally, the one forensic method that passed scrutiny was developed not by law enforcement to aid investigation of crimes but by a scientist working in an academic laboratory.