Television shows like CSI have given us, the channel-surfing American public, an almost mystical faith in the crime-solving abilities of DNA. We expect the presence of foreign DNA in the victim's bite wound to nail the perp, and the absence of any traces of the stuff to help absolve the innocent. That seems to have been the reasoning, anyway, behind Boulder District Attorney Mary Lacy's startling 2008 "exoneration" of John and Patsy Ramsey, declaring their lack of any involvement in the still-unsolved 1996 murder of their six-year-old daughter, JonBenet; the presence of an unknown male's DNA in the girl's underwear points to an intruder as the killer, Lacy said.

See also: JonBenet Ramsey: How the Investigation Got Derailed -- And Why It Still Matters

But as discussed in this week's feature story about how the Ramsey homicide investigation turned into a train wreck, drawing conclusions about a phantom perpetrator based on the microscopic amounts of "touch" DNA Lacy is talking about is a hazardous business.

As Dan Krane, a nationally known biochemist and DNA expert, told me, "Someone has optimistically concluded that they can have confidence in these results, and that just seems misguided."

To understand Krane's reservations about the mystery DNA in the Ramsey case, consider the Phantom of Heilbronn, a cautionary tale that future crime-tech wannabes now learn early in their training.

From 1993 until 2009, police agencies across Austria, France and Germany were baffled by the tantalizing clues left behind by a master criminal and serial killer known only as "The Woman Without a Face." Her DNA kept turning up in the oddest places: on a kitchen drawer in Freiburg, Germany, near the corpse of a 61-year-old man. On a toy pistol found after the robbery of gemstone traders in Arbois, France. On a syringe full of heroin in the woods outside Gerolstein, Germany. On a cup at another murder scene, on a cookie in a trailer that had been burglarized, in a car used to transport three dead Georgians.

The police didn't know much about the woman other than that her mitochondrial DNA pointed to Eastern European or Russian origin. And she seemed to get around, having been linked to six murders, including one of a police officer in Heilbronn, Germany.

A special task force was formed to try to find this elusive predator. A reward was offered for information, the sum eventually soaring to 300,000 euros.

Then, in 2009, the mystery woman's DNA turned up on the burned body of a male refugee in France. That prompted investigators to look closer at how the DNA got there. The answer was in the swabs used by numerous police agencies to take DNA samples -- they'd been contaminated at the factory. Which employed many women from Eastern Europe.

The samples in the Ramsey case are weak traces -- and possibly the result of cross-contamination. In addition to the three "hits" for touch DNA on the victim's clothing, there are five other unknown trace DNA samples found on the body, cord and garrote that don't match each other. Most of them are only partial profiles, too incomplete to put in a database, and there's no way of telling if they're from blood, saliva or some other tissue, or if their presence predates the crime. Yet in her 2008 letter to John Ramsey offering an apology for putting his family under the umbrella of suspicion, Lacy said she was "comfortable" that the trace DNA "is the profile of the perpetrator of this murder."

Every crime scene contains some unexplained crud -- a fingerprint, a hair, a smudge that seems out of place. A good defense attorney can make an entire alternate suspect out of such "clues." It's rare for the prosecution to do the same thing, but in the Ramsey case, much of the investigation has been devoted to chasing phantoms.