On TV crime shows like CSI, NCIS, and Law & Order, science gets the bad guys.
In real life, "science" often ensnares the innocent.
Former NYPD Detective Harry Houck gets annoyed when TV shows make forensic science look infallible.
"You watch a detective get down and look at a body (and say), 'He's been dead for three hours now... (H)e ate dinner four hours ago,'" scoffs Houck. "I can't do that."
On TV, experts identify killers by their bite marks. In real life, experts claimthey can do that.
The TV show Cold Case Files covered the trial of Alfred Swinton. He was convicted of murder because a bite-mark expert said his teeth matched a bite on the victim.
"A perfect match!" said Dr. Gus Karazulas, the "forensic odontologist" whose testimony clinched the conviction.
Karazulas sounded impartial and objective. "A forensic scientist is not on the side of the prosecutor or defense," he said on Cold Case Files. "We look at the evidence."
But Swinton was innocent. Lawyer Chris Fabricant helped get him released from jail by doing a DNA test, a much more reliable, less subjective form of science.
Fabricant scoffs at bite-mark testimony: "The doctor was just wrong. It's an unreliable technique."
The more room there is for an expert witness's unique interpretation of the data, the more that can go wrong, says Fabricant. "Bite mark is similar to you and I looking at a cloud. I say to you, 'John, doesn't that cloud look like a rabbit?' And you say, 'Yeah, Chris, I think that does look like a rabbit.'"
That kind of junk science puts innocent people in jail.
I told Fabricant that I assumed most people in jail are guilty. Also, many people say crime is down because aggressive law enforcement has locked so many people up.
"If you think that maybe even 1 percent of convicted defendants may be innocent," replied Fabricant, "we have 2.6 million people in prison today, (so) we are talking about tens of thousands of (innocent) people!"
Fabricant works with the Innocence Project, a group that works to get innocent people freed from prison. Through DNA evidence, the project's lawyers have helped free 191 people.
That confident bite-mark expert who got Swinton convicted now admits he was wrong. "Bite mark evidence is junk science," he told us via email. He resigned from the American Academy of Forensic Sciences.
But police still trust bite marks.
"Let's say one tooth is missing in the front" of a bite mark, explains Houck. "You've got to go, well, our suspect's got one tooth missing in the front. That's pretty good!"