Glossip, 61, is on death row for the 1997 murder of Barry Van Treese at the Best Budget Inn in Oklahoma City, which Van Treese owned and Glossip managed. It is undisputed that Glossip did not swing the bat that killed Van Treese. That was Justin Sneed, a drug-addled handyman whose testimony against Glossip was the only direct evidence connecting him to the murder.

Glossip was found guilty of paying Sneed to kill Van Treese and first sentenced to death in 1998. That sentence was overturned due to what a state court deemed ineffective legal counsel, and he was sentenced again in 2004.

Nearly 20 years later, an independent investigation commissioned by Oklahoma legislators concluded that Glossip’s conviction should be set aside. A separate investigation commissioned by the state attorney general reached the same conclusion last year.

“Each investigation found that Glossip’s prosecution had been riddled with misconduct, errors, and omissions from the start — from a deficient police investigation to the destruction of critical physical evidence to the suppression of substantial exculpatory evidence,” his attorneys told the Supreme Court in filings ahead of Wednesday’s argument.

Glossip has been scheduled for execution nine times. He was hours from being executed in 2015 when prison officials discovered they had received the wrong lethal drug, a mistake that led in part to a seven-year moratorium on executions in the state.

Glossip’s cause has brought together a bipartisan alliance, including members of the Oklahoma Death Penalty Review Commission and former Virginia attorney general Ken Cuccinelli.

Two former solicitors general are arguing in support of Glossip’s position on Wednesday. Seth B. Waxman, who was solicitor general during the Clinton administration, is representing Glossip. Paul Clement, who was solicitor general during the administration of George W. Bush, is representing Oklahoma Attorney General Gentner F. Drummond (R).

Because the attorney general now opposes putting Glossip to death, the Supreme Court appointed Christopher Michel — a former law clerk to Chief Justice John G. Roberts Jr. and Justice Brett M. Kavanaugh — to argue in support of a ruling from Oklahoma’s top state court that the execution should go forward.

Even though Drummond is Oklahoma’s top law enforcement officer, he lacks the authority to stop Glossip’s execution on his own.

The Oklahoma Court of Criminal Appeals last year unanimously refused to accept Drummond’s “confession of error” and order a new trial for Glossip. The court said the prosecutorial misconduct did not rise to the level of a constitutional violation of Glossip’s rights and that Glossip had not shown that a jury would have reached a different conclusion had prosecutors disclosed the evidence in advance of his trial.

In its filing, the attorney general’s office said the state court’s decision sends a “troubling message that it will cling to its past decisions even in the rare situation in which a State’s chief law officer concludes that a fresh review is needed. That message has no valid place in our system of justice, least of all in a capital case.”

Michel, the lawyer appointed to argue in support of the state court’s ruling, urged the justices to dismiss the case, saying the Supreme Court does not have jurisdiction to decide the state matter and the governor has the power to grant clemency.

The state’s pardon and parole board split 2-2 on Drummond’s request for intervention; a vote in Glossip’s favor would have been necessary to recommend that Gov. Kevin Stitt (R) commute his sentence to life without parole.

An earlier death penalty case at the Supreme Court carried Glossip’s name, though it was focused on the drugs used by Oklahoma for executions and larger questions about how capital punishment is carried out in the United States.

In 2015, the justices ruled 5-4 against Glossip and other death-row inmates who said Oklahoma’s use of a sedative called midazolam has resulted in troubling executions that violate the Constitution’s prohibition on cruel and unusual punishment.

Justice Samuel A. Alito Jr. wrote for the majority that the inmates had failed to identify an alternative method of execution that would carry a lesser risk of pain.

The court’s composition has changed since then. Among those still on the bench, Alito was joined in his ruling by Roberts and Justice Clarence Thomas. The other justices in the majority were Anthony M. Kennedy, who has since retired, and the late Antonin Scalia.

Two justices who are no longer on the bench — Stephen G. Breyer and Ruth Bader Ginsburg — used their dissent in the case to say it was time for the court to take another look at whether the death penalty could ever be carried out in accordance with the Constitution. Justices Sonia Sotomayor and Elena Kagan, who also dissented, are still on the bench.

When the Supreme Court more recently put Glossip’s execution on hold in May 2023, there were no noted dissents to the court’s order.

The justices are hearing Glossip’s case at a time when the death penalty has markedly declined. Executions and death sentences are both significantly down from what they were in the late 1990s.

But while some states have paused executions or abandoned capital punishment outright, it is still consistently used in other places — including Texas and Oklahoma, the two states that have carried out the most executions since 1976, according to the Death Penalty Information Center, a Washington-based group. Last month, those two states — along with South Carolina, Missouri and Alabama — carried out a combinedsix executions over an 11-day period.