The court is considering the case of Texas death row inmate Hank Skinner, who was an hour away from a lethal injection when the justices stepped into the case.
Skinner says he did not kill his girlfriend and her two sons 17 years ago. Skinner says considerable evidence that was not tested at the time of his trial, on the advice of his lawyer, could help exonerate him.
If the court rules against him, Skinner probably will be put to death without the material ever being tested despite a Texas state law intended to allow defendants to do DNA testing on evidence that was not performed before their convictions.
But neither Skinner's guilt nor the DNA evidence itself is the central issue in the legal case before the Supreme Court.
Instead, the court is deciding whether Skinner can use a federal civil rights law to try to persuade a federal judge to order the prosecutor to turn over two knives, fingernail clippings from Skinner's girlfriend and other evidence found at the crime scene that has never been tested. Should Skinner and his new defense team prevail on all those steps, they would then have DNA tests done on the material.
So the justices engaged in a highly technical argument without referring to the murders or the evidence and made only a couple of mentions of why the case matters.
"What he wants is the DNA," Justice Stephen Breyer said. "He thinks it's going to be exculpatory. He doesn't know that till he gets it."
Skinner narrowly avoided execution after state courts ruled against him and lower federal courts dismissed his claims. In March, he was spared lethal injection an hour before he was to go to the death chamber when the justices decided they wanted time to look at his appeal.
A jury deliberated just a few hours before convicting Skinner of the three killings. He acknowledged being inside the house in the Texas Panhandle where the killings took place. A trail of blood led police to his hiding place in a closet in a trailer a few blocks away. The blood of at least two victims, testing showed, was on his clothing.
But Skinner has maintained his innocence. He says he was passed out from a potent mix of vodka and codeine at the time of the killings. He points to his girlfriend's uncle, now dead, as a possible suspect and says that testing might back his claim.
Prosecutors argue that Skinner is trying to game the system. They say he's asking for the testing now as a last-ditch attempt to postpone execution after passing up testing on the other evidence at trial because his lawyer feared it would further incriminate him.
Skinner's trial lawyer was a former district attorney who had prosecuted Skinner for car theft and assault. The lawyer has defended the decision to forgo testing, though he now says the additional tests should be done.
Some prosecutors have argued that a high court ruling for Skinner would lead to an explosion of similar lawsuits from prison inmates across the country.
But a study by New York University law professor Colin Starger found that just 21 prison inmates sought access to DNA evidence by filing federal civil rights complaints from 2000 to 2008.
A decision is expected by spring.
The case is Skinner v. Switzer, 09-9000.