Michael Mermel, chief of the criminal division for the Lake County, Illinois state's attorney's office, is rather unimpressed by the value of exonerating DNA evidence, especially when it conflicts with good ol' eyewitness testimony, confessions, even bite-mark evidence.

For example, six years ago, Mermel dismissed DNA tests showing that the semen found in the underwear of a 68-year rape victim didn't belong to the man convicted of the crime.  Bernie Starks had been serving time for the rape since 1986.  Now if the DNA had come from the woman's vagina, Mermel argued at the time, "I would be standing over there advocating the side that the defense has in the case." 

Actually, no he wouldn't.  Three years later, a missing rape kit from the case turned up.  It included a vaginal swab containing semen, and a DNA test on the semen again excluded the man convicted of the crime.  Mermel again refused to concede, this time arguing that the woman must have had consensual sex with another man at about the same time of the rape.

When DNA testing on an 11-year-old rape and murder victim excluded his suspect, Mermel said the more likely explanation there too was that the girl had been sexually active—not that he could possibly be charging the wrong guy.

But this one beats all:

And, just recently, when lawyers for the man charged in the killing of his 8-year-old daughter and her 9-year-old friend said in court that DNA evidence from semen excluded him as the perpetrator, the Lake prosecutor had another explanation.

Mermel said DNA may have gotten inside the 8-year-old's body as she played in the woods at what became the crime scene—a place where Mermel said some couples go to have sex. The girl was found fully clothed.

That's some mighty potent semen.