Richard Glossip was about to be executed in 2015, saved at the last minute only because of a mix-up in the lethal injection drugs Oklahoma had planned to use.

On Tuesday the U.S. Supreme Court tossed his murder conviction and death sentence and ordered a new trial, saying too many questions had arisen about whether he was actually guilty of the murder for which he almost paid with his life.

Glossip had admitted he helped conceal the murder after the fact but had steadfastly denied any involvement in the actual slaying. Years after his conviction, Oklahoma prosecutors disclosed boxes of evidence that had been withheld that showed the convicted killer, who had fingered Glossip as his accomplice, suffered from bipolar disorder and gave false testimony at Glossip’s trial.

The state’s Court of Criminal Appeals said that wasn’t enough to overturn the conviction but the Supreme Court said Tuesday it was.

“Glossip is entitled to a new trial,” wrote Justice Sonia Sotomayor, who wrote the key opinion for the majority.

She was joined by Chief Justice John G. Roberts Jr. and Justices Elena Kagan, Brett M. Kavanaugh and Ketanji Brown Jackson. Justice Amy Coney Barrett filed a mixed opinion and Justices Clarence Thomas and Samuel A. Alito Jr. dissented, saying they would not have overturned the lower court’s ruling.

Oklahoma Attorney General Gentner Drummond, whose own review had exposed serious problems in the prosecution, called the ruling “a fresh opportunity to see that justice is done.”

“I have long maintained that I do not believe Mr. Glossip is innocent, but it is now an undeniable fact that he did not receive a fair trial,” he said.

Death penalty opponents said Glossip’s case exposed serious problems with the capital punishment system itself.

“Even after it became clear that prosecutors had buried exculpatory evidence, the machinery of the death penalty continued to grind on for years,” said Brian Stull, at the American Civil Liberties Union. “This case shows that we cannot trust the state convict and imprison only the innocent, let alone to ensure that innocent people are never strapped to the execution table.”

The case stemmed from the murder of Barry Van Treese, owner of the Best Budget Inn in Oklahoma City.

One employee, Justin Sneed, confessed to beating the owner to death. In exchange for prosecutors forgoing the death penalty, Sneed agreed to testify that Glossip had orchestrated the killing, Glossip denied that, though he admitted to misleading police about the slaying.

He repeatedly rejected plea deals, saying he wanted to prove his case.

He was convicted in 1998, but had that overturned by the state Court of Criminal Appeals in 2001. He was tried again in 2004 and convicted.

Both times, Sneed’s testimony was the only thing tying him to the actual killing, Justice Sotomayor said.

That conviction survived the state appeals court, albeit narrowly.

In 2015, Glossip and other Oklahoma death row inmates had their challenge to the state’s choice of lethal injection drugs heard at the Supreme Court. The justices, in a 5-4 ruling, upheld the state’s execution protocol.

Justice Sotomayor’s ruling Tuesday was based heavily on Sneed’s questionable testimony and how much it skewed the jury’s perceptions of what happened. She said later evidence showed Sneed had medical conditions that, if the jury had known about them, could have changed their understanding of the chain of events.

“For these reasons, we conclude that the prosecution’s failure to correct Sneed’s trial testimony violated the Due Process Clause,” she wrote.

Justice Thomas said her ruling “stretches the law at every turn” in order to help Glossip.

He said federal courts shouldn’t have jurisdiction in the case, and he said Justice Sotomayor’s worries about the trial were based on “patently immaterial testimony about a witness’s medical condition.”

• Stephen Dinan can be reached at sdinan@washingtontimes.com.