Seattle, 1982. An unknown suspect murdered a 13-year-old girl. The investigation went cold for 20 years with no leads -- until officers tricked the suspect into mailing them a letter.
They wanted his saliva, loaded with his DNA, on the envelope.
Police cracked the case, using the genetic imprint from the suspect, John Athan -- evidence he unwittingly sent them through the mail.
DNA -- it's a key clue in TV dramas, in addition to helping crack old cases in the real world. Today, all over the country, detectives are re-examining evidence collected at the time of the crime, comparing it to so-called "abandoned" DNA, like the saliva on Athan's letter.
Detectives are solving crimes using sweat collected from a steering wheel, or saliva from a discarded cigarette butt. In a Detroit case, it was spit on a leftover cinnamon roll that sent a man to jail for car theft.
"People leave parts of themselves all over all of the time," said Seattle Police homicide detective Nathan James. "DNA is like fingerprints, only better. It is just more precise than fingerprints. At this point it is more reliable than fingerprints."
In Buffalo, N.Y., investigators solved a triple homicide after police trailed a suspect to a restaurant. When Altemio Sanchez finished dinner, they scooped up his dirty dishes.
"We got the DNA from him off of a coffee cup," said Erie County, N.Y., district attorney Frank Clark. "That's how we got the sample, the known sample that we could apply against the DNA found from our homicide victims."
Clark told ABC News that investigators look to find DNA in every imaginable place. "I mean, we're looking at cigarette butts, we're looking at chewing gum. We're looking at shirt collars. We're looking at the insides of gloves. Everything you used to dust for fingerprints for, now you look for DNA."
If a suspect drinks from a cup and tosses it away, detectives like Dennis Delano of the Buffalo Police Department can easily work with evidence left behind. "Anytime that you drink out of something, you will leave biological fluid. They can get a full DNA profile from [a] cup," he said.
Delano uses new technology to solve old crimes, following suspects just to get their abandoned DNA.
His department trailed a murder suspect for weeks, waiting for him to leave some of the valuable genetic material behind. The suspect eventually spat on the parking lot beside his house, and police moved in to collect their evidence.
Investigators say they matched DNA in the saliva with a hair found at a crime scene back in 1974, when Barbara Lloyd was raped and killed. They charged Leon Chatt, the spitter, with the murder. Chatt has pleaded not guilty, and his attorney contends a DNA match alone does not convict his client.
But the sly tactics worry privacy experts, who charge that the technique allows police to circumvent the legal system.
"What troubles me is that the police collected DNA, analyzed DNA, of an individual without any judicial intervention. No judicial authorization. No probable cause. No warrant," said Doug Klunder, privacy project director for the American Civil Liberties Union of Washington State.
"And I don't believe that the police should be able to collect somebody's private, very intimate information, their DNA, just because they have a hunch that it will be useful," Klunder continued.
Prosecutors, however, say it's simply a new twist on an old method.
King County, Wash., senior deputy prosecutor Catherine McDowall compares the technique to police taking fingerprints from a soda can given to a suspect during a police interview. "I think certainly anything that anyone exposes to the public is fair game for police to use in an investigation," she said.
"The only difference in this case is that they [police] are taking biological evidence and getting essentially what is just a genetic fingerprint from a suspect," McDowall added.
DNA also protects the innocent, prosecutors contend. Sanchez, the Buffalo murder suspect, pled guilty after DNA indicated he was the killer in his triple homicide case
But his DNA also matched evidence collected from the scenes of a notorious series of brutal rapes. Another man, Anthony Capozzi, had been in prison for 22 years, serving time for those crimes which he didn't commit.
Whether the suspects are guilty or innocent, cops like Delano say they'll follow the DNA trail wherever it leads.