Can DNA evidence solve a 30-year-old crime?

The 1984 sexual assault and murder of a 14-year-old Claire Hough on a California beach became a cold case after DNA swabs failed to provide any matches. In 2012, a more sensitive technique was used to analyze DNA found on the victim’s body and in a vaginal swab. DNA tests revealed two matches. DNA samples on her body matched Ronald Tatro, a man with a history of sexual and violent crimes who had died in a suspected suicide on the 27th anniversary of the discovery of Hough’s body. A second suspect, Kevin Brown, was found to be a DNA match for semen samples found on the vaginal swab of the victim.

Kevin Brown had been a crime lab employee with San Diego Police Department, the lab that investigated Hough’s case, from 1982 until his retirement in 2002. Although Brown had a reputation for enjoying strip clubs, participating in boudoir photography, and making offensive sexual comments, there were doubts of Brown’s guilt. There were no connections between Brown and Tatro, and Brown maintained his innocence throughout the investigation. As a result, the fallibility of the DNA testing process was brought into question. While contamination by crime lab employees can occur, the potential contamination of a sample by Brown’s semen was more questionable than stray skin samples or saliva samples.

“[T]he process of “differential extraction,” which is supposed to isolate sperm cells from non-sperm cells for analysis, fails up to half of the time. If differential extraction failed in Brown’s case, his skin cells or saliva could have gotten onto the Hough vaginal swab, and nobody would have been the wiser. The technician might have believed he was analyzing DNA that came from semen.”

Even if the differential extraction process had been carried out correctly and Brown’s semen was actually on the potentially contaminated sample, there is another explanation for how Brown’s semen could have ended up on the swab:

“To verify that evidence tests are set up correctly, criminalists analyze reference samples, also known as standards. Many of these standards are purchased from laboratory-supply companies. But in the 1980s, analysts frequently turned to a fresher, cheaper source. ‘The semen standards that we used were from ourselves,’ Stam says bluntly. Criminalists’ using their own semen was a convenient, common shortcut, but one that, unbeknownst to them at the time, presented a high risk of contamination. ‘They had Brown’s pure, amplified DNA around,” Hampikian says.Knowing that Brown’s semen was present in the lab, Stam offered a guess as to how it could have gotten into the Hough evidence. ‘If someone cut the [Hough] swab with the same pair of scissors that they used to cut Kevin’s swab for use as a standard, who knows?’ ”

Unfortunately, even if Brown could have his name cleared, it would be too late. Knowing that SFPD suspected Brown and were close to arresting him, Brown grew anxious and depressed. He committed suicide on October 20, 2014 before facing arrest or trial. Experts note that this case highlights the problems with DNA evidence in that once someone is implicated, it is extremely difficult to convince others, particularly jurors, that a DNA match could be faulty.

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