Supreme Court weighs key testimony that underpins death row inmate's conviction

The Supreme Court on Wednesday probed whether death row inmate Richard Glossip's murder conviction should be thrown out because a key witness lied in court and prosecutors withheld information about him.

As Justice Elena Kagan put it, the state’s most important witness, Justin Sneed, was “exposed as a liar.”

It is an unusual death penalty case in which the attorney general of Oklahoma, Republican Gentner Drummond, has sided with a defendant.

Based on almost two hours of oral argument, it appeared the court could rule in Glossip's favor, although it could stop short of tossing out the conviction and instead order a new hearing on recently disclosed information about the conduct of prosecutors.

Glossip, who is now 61, was convicted of arranging for the murder in 1997 of his boss at the Oklahoma City motel where they worked.

But his conviction rested largely on the testimony of Sneed, who carried out the 1997 murder. Sneed, who pleaded guilty and avoided a death sentence, testified that Glossip had hired him to kill motel owner Barry Van Treese.

Drummond made the rare decision to back Glossip’s appeal following an investigation into the case. The state has stopped short of agreeing with Glossip’s claim that he is innocent.

The Supreme Court has a 6-3 conservative majority that generally backs the death penalty but occasionally steps in when there has been a clear miscarriage of justice.

The latest case focuses on claims that prosecutors had withheld information about Sneed and that he had given false testimony at trial.

During oral arguments, the justices debated the significance to the case of prosecutors knowing but not disclosing at Glossip’s second trial in 2004 that Sneed had been diagnosed with bipolar disorder and prescribed lithium after his arrest.

Sneed also falsely testified that he had never seen a psychiatrist.

Drummond concluded that as Glossip's conviction rested significantly on Sneed's credibility, it should not be sustained.

The new information, Justice Brett Kavanaugh said, showed that Snead had an incentive to lie and had done so "creating all sorts of avenues for questioning his credibility."

Despite Drummond's findings, an Oklahoma appeals court upheld the death sentence last year and the state’s pardon and parole board voted against granting Glossip clemency.

Kagan was particularly scathing over the Oklahoma court ruling, at times critiquing individual paragraphs.

When a lawyer appointed by the court to defend the lower court ruling acknowledged her criticism but suggested that did not warrant overturning it, Kagan responded: "I haven't even started."

Justice Clarence Thomas appeared most inclined to leave the conviction in place, suggesting that there were flaws in the investigation. He said that the prosecutors who had worked on the case, Connie Smothermon and Gary Ackley, had not been given a proper opportunity to give their side of the story.

They wrote a letter questioning the new findings that was attached to an amicus brief filed by relatives of Van Treece urging the court to uphold Glossip's conviction.

But as the justices discussed in court, the letter is not part of the official court record. For the claims made by the two prosecutors to be considered in full, there would need to be a new evidentiary hearing.

"It would seem that because not only, you know, their reputations are being impugned, but they are central to this case," Thomas said.

The Supreme Court previously signaled an interest in Glossip’s case by stepping in last year to prevent him from being executed. The court also blocked Glossip’s execution in 2015 in separate litigation over the state’s lethal injection procedure.

Eight states including Texas and Utah have urged the Supreme Court to uphold the Oklahoma court ruling. Utah, joined by six other states, filed a brief arguing that the Supreme Court had no business intervening in the case, which was focused on Oklahoma state law.

Texas filed a separate brief saying that there was no reason for the Oklahoma court to rule in favor of an inmate just because the state asked it to.

Justice Neil Gorsuch did not participate in the case having previously recused himself when the court agreed to take it up. The court has not given a reason but it likely relates to his previous role as a judge on the 10th U.S. Circuit Court of Appeals, which hears cases from Oklahoma. If the court is divided 4-4, as is possible, then the state court ruling against Glossip would remain in place.

This story first appeared on NBCNews.com. More from NBC News:

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