"It's like having an 18-wheeler driving on your chest. And you believe the only way to get that weight off your chest is to tell the police whatever they want to hear," says Tankleff.
But 14 years later, as "48 Hours" Correspondent Erin Moriarty reports, Tankleff and his family now say they can prove he's innocent with a mountain of new evidence, including what may be the real murder weapon and a parade of witnesses. On Tuesday they will ask a judge for a new trial based on new evidence.
Glenn Harris says he drove the real killers to the Tankleff home for what he thought was a burglary.
"I knew something happened, that something more than a burglary happened," says Harris. "It appeared there was an encounter of some sort."
One of the alleged killers was a career criminal that Tankleff's family believes was hired by Seymour Tankleff's business partner: a man with a motive. He was deeply in debt to Tankeleff ... and the last person to see the couple alive.
And then there's that confession: the lead detective on the case admits he tricked the defendant, claiming Martin Tankleff's father named him as the killer right before he died.
"Yes, I lied to him," says detective James McReady.
Tankleff, just barely 17 at the time, began to believe he might have done it.
"Detective McCready said that my father said it was me and I believed that," he says.
Now 32, Tankleff is asking for a second chance.
To get a new trial, Tankleff has to prove that this new evidence would have convinced the original jury to find him not guilty, a standard that is easy enough to understand but in reality very difficult to meet.
The problem, the family says, is the decision -- and Tankleff's future -- are in the hands of Suffolk County, New York authorities - the same people who used a coerced confession and shoddy evidence in the first place.
"There was an incredible rush to judgment," says Howard Asness. "The Suffolk County police and the DA's office, they figured, 'Oh look at this, we've settled this terrible crime in less than a day.' And that was that."
With the odds stacked against them, the Tankleff family hopes for justice they say they've never gotten. But police and prosecutors say guilty means guilty. And unless a judge re-opens his case, Tankleff will likely spend the rest of his life in prison.