WASHINGTON — The Supreme Court on Wednesday will weigh whether inmate Richard Glossip's murder conviction should be thrown out — an unusual death penalty case in which the attorney general of Oklahoma has sided with a defendant.

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.

Oklahoma Attorney General Gentner Drummond, a Republican, 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.

If Glossip wins, the Supreme Court, which has a 6-3 conservative majority that generally backs the death penalty, would order that his conviction be thrown out and the case sent back to a lower court for a new trial.

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.

Questions about Glossip's prosecution rest mostly on concerns about key testimony provided by Justin 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.

But it has since emerged that prosecutors had withheld information about Sneed and that he had given false testimony at trial.

"The newly disclosed evidence confirms that the state knew Sneed’s testimony was false and did nothing to correct it," Glossip's lawyers wrote in court papers.

The independent investigation ordered by Drummond found among other things that prosecutors knew but did not disclose 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 centrality of Sneed’s testimony to the murder charged cannot be overstated," Drummond's lawyers said in court papers.

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.

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.

Family members of Van Treese also urged the court to uphold the conviction, saying that the case was a "cautionary tale" of the potential dangers of courts relying too much on a state official's confession of error.

Justice Neil Gorsuch is not expected to 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.