DNA evidence has been widely embraced as a powerful forensic tool to prove a defendant’s guilt or innocence. In Lake County, Il., reports the Chicago Tribune, authorities have sometimes pressed for convictions even when the DNA doesn’t match a suspect. When DNA evidence excluded a man convicted in the rape and battery of a 68-year-old woman, the prosecutor’s criminal division chief Michael Mermel suggested the victim had consensual sex with someone else. When DNA evidence excluded a man in the rape and murder of an 11-year-old girl, Mermel suggested that the girl may have been sexually active. The DNA, he said, was a “red herring.” He argues that other evidence, mainly confessions and witness identification, carry greater sway than the genetic material.
That attitude startles some DNA experts. “The vast majority of prosecutors in the United States generally are willing to walk away from a case where DNA excludes a suspect,” said Joshua Marquis, an Oregon prosecutor and member of the board of directors of the National District Attorneys Association. Said another expert, William Thompson of the University of California at Irvine, “It’s just amazing how convincing DNA can be if it supports your case and how unconvincing it is when it doesn’t support your case.” Defending his office’s approach, Mermel said Lake prosecutors believe in DNA “when it is forensically significant.”