For the detective, it looked like a sure thing. The 58-year-old suspect with a prior sex-crime conviction had confessed to raping his young niece, reports the Seattle Post-Intelligencer. DNA evidence from the 10-year-old girl’s underwear would be the clincher. Charged with child rape, the road-crew worker faced up to 26 years in prison — until authorities learned of startling test results coming out of the Washington State Patrol’s Tacoma crime lab. The genetic evidence excluded the victim’s uncle and pointed to an unknown man. Prosecutors offered a deal. The defendant pleaded guilty to a lesser charge of child molestation, shaving a decade off his sentence.
Later, the lab made an embarrassing discovery. A forensic scientist had bungled the test, accidentally contaminating the child’s clothing with DNA from another case. DNA contamination and errors at the State Patrol crime labs are recurring problems, an investigation by the Post-Intelligencer found. Forensic scientists contaminated tests or made other mistakes while handling DNA evidence in at least 23 cases involving major crimes over the last three years, according to patrol and court records. “The amazing thing is how many screw-ups they have for a technique that they go into court and say is infallible,” said William C. Thompson, a forensic expert and professor of criminology and law at the University of California-Irvine, who reviewed the Washington State incidents. “What we’re seeing in these 23 cases is really the tip of the iceberg.”