Every now and then, although much less recently, a reporter asks me the inane question, “Is DNA a silver bullet?” While the obvious answer is “no,” the follow-up is always, “DNA will never replace a thoughtful, creative detective with the proper resources.” No one has ever disagreed with me on that. That is however, the positive spin on the answer. Another approach is, “Regardless of how good the technology is, it is ultimately a system run by human beings—mistakes can and will be made.” Does the case of a certain Heisman trophy winner come to mind?

Last fall, the British newspaper The Guardian ran a lengthy article on the most significant serial killer in Europe. The killer, dubbed “the woman without a face” was implicated in six murders, including the murder of a female German police officer shot in the back of the head while she sat in her patrol car. The killer was not just a brutal executioner though, she was a thief (DNA was found at numerous burglary scenes) and a drug addict (DNA was found on a heroin syringe). She was a frequent traveler, her DNA being found at crime scenes in Germany, Austria, and France. And her weapon of choice varied (DNA was found on a stone used to smash a victim’s face).

The “woman without a face” was law enforcement’s worst nightmare—elusive, seemingly indiscriminant, violent, and well traveled. DNA samples were taken from 3,000 homeless women believed to be drug users. A reward of €100,000 ($135,000) was posted. And German, Austrian, and French authorities spent millions of Euros on the investigation.

In the course of the story, the reporter interviewed a prosecutor (note this isn’t just about the police) in charge of the investigation. When talking about the status of the unsolved case, the prosecutor said, “There are still no witnesses, and no other evidence. All of us on the various teams talk to each other two or three times a month. We meet, we e-mail, but mostly we wait for another report saying the same DNA has turned up.”

Uh-oh. That’s a bad statement.