The execution of Marcellus Williams brings a new test of the Supreme Court’s approach to the death penalty

The Supreme Court’s split decision this week, allowing Missouri to execute a man for a 1998 murder even though his conviction was challenged by prosecutors, has put the court’s approach to the death penalty under renewed scrutiny.

Marcellus Williams, who was convicted in the 2001 killing of former newspaper reporter Felicia Gayle, was executed Tuesday evening, just over an hour after Supreme Court conservatives declined to intervene over objections from the three liberal justices. The execution was sharply criticized by the NAACP and other groups, which claimed Williams was innocent.

Part of that backlash was directed at the Supreme Court, which for decades rarely granted last-minute pardons to death row inmates. According to the Death Penalty Information Center, the court has intervened twice in the past two years to stop executions in more than two dozen summary cases.

“It’s very concerning how the Supreme Court handles capital cases these days,” said Cliff Sloan, a professor at Georgetown Law School who won a major Supreme Court case in 2017 involving a mentally disabled death row inmate. “In any fair and just society, a free-standing claim to innocence should be recognized as an important constitutional right.”

When dissenting opinions are found in capital case petitions, they invariably come from the court’s liberal wing. And as the appeals enter the court’s docket for further consideration, the outcome tends to divide liberals and conservatives into separate camps.

“The Supreme Court has a limited role in death penalty cases,” said Paul Cassell, a law professor at the University of Utah who is representing the family of a victim in another death penalty case before the Supreme Court this year. These cases, Cassell said, “are handled primarily by state agencies with limited oversight from the federal courts.”

The death penalty will continue to be a major issue at the Supreme Court in the coming weeks, with several defendants up for consideration when the justices meet on Monday to consider appeals that have piled up over the summer. One involves an Oklahoma woman who was convicted of murdering her husband. She says prosecutors sexually shamed her during her trial, calling her a “bitch” in court and holding up her underwear to the jury.

Another case involves an Alabama man who claims he is mentally disabled and therefore ineligible for execution under Supreme Court precedent.

The Glossip appeal is due to be heard next month

The court is already set to hear arguments about Richard Glossip, an Oklahoma death row inmate. The case concerns the 1997 murder of Barry Van Treese, the owner of an Oklahoma City motel. Justin Sneed, who worked at the motel, was convicted of that murder, but in exchange for avoiding a death sentence, he accused Glossip of setting up Sneed and to have commissioned the execution of the crime.

Glossip is asking the court to overturn his conviction after the state admitted its case was riddled with errors. For example, prosecutors failed to disclose records showing that Sneed, the key witness against Glossip, was being treated for a psychiatric illness. Oklahoma Attorney General Gentner Drummond, a Republican who defends the death penalty, sides with Glossip, citing “disturbing evidence of serious prosecutorial misconduct.”

Williams, whose execution sparked outrage on social media, sought to compare his situation to that of Glossip and noted that prosecutors had also raised serious concerns about his trial. Among other things, St. Louis County Prosecutor Wesley Bell said his predecessor contaminated the murder weapon by handling it without gloves. Bell, a Democrat, is running for Congress.

In Williams’ case, unlike Glossip’s case, the state was still firmly in favor of execution. Missouri Attorney General Andrew Bailey, a Republican running for re-election, dismissed Williams’ theory that DNA testing of the knife might have exonerated him if prosecutors had handled it more carefully. Instead, Bailey said, “The evidence was consistent with a crime scene investigator’s statement that the killer was wearing gloves, based on glove marks left at the crime scene.”

The two cases overlap so much that some believe the outcome for Williams could portend trouble for Glossip.

“When state courts fail disastrously to address these issues, you expect the U.S. Supreme Court to step in, especially when you have an (appeal) filed jointly by the prosecution and defense,” Robert said Dunham, director of the Death Penalty Policy Project, who has also represented death row inmates on the Supreme Court. “It will be very difficult to find justification for what happened.”

Cassell, who is representing the Van Treese family in the gossip appeal, said those supporting the defendant’s claims have been “willfully blind to the facts of the case at hand” and based their concerns on “a few excerpts from the notes of the case.” “The public prosecutor’s office would have supported.”

The Supreme Court did not explain why it rejected Williams’ request. The court’s three liberals — Justices Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson — noted her dissent but also did not write to explain their position.

Sotomayor, in particular, has expressed opposition to the death penalty in some previous appeals.

When the Supreme Court allowed Alabama to execute Kenneth Smith with nitrogen gas in January, Sotomayor wrote a strongly worded dissent.

“Because Smith failed to kill him on the first attempt, Alabama chose him as a ‘guinea pig’ to test an execution method that had never been tried before,” she wrote. “Once the nitrogen flows into the mask, his executioners will not intervene and remove the mask, even if Smith vomits inside it and chokes on his own vomit.”

Smith was executed at the end of January.

In a landmark 1972 decision, the Supreme Court ruled that the way states administered the death penalty constituted cruel and unusual punishment in violation of the Eighth and 14th Amendments to the Constitution. While the decision overturned hundreds of death sentences, it did not ban the practice entirely. Instead, the majority of states enacted new laws that restored executions in a manner consistent with the court’s decision.

The court’s general reluctance to consider last-minute appeals to the death penalty stems in large part from its role within the federal judiciary. The judges look for clear errors by the lower courts and not for new evidence from the defendants.

The Supreme Court’s approach to death penalty appeals is to “correct serious misapplications of constitutional law by America’s state court systems,” said Seth Kretzer, a Texas lawyer who has represented death row inmates in the Supreme Court.

The court, Kretzer said, “will not stop an execution in an individual case just because the inmate presents new evidence at the last minute.”

New cases in the pipeline

The Supreme Court will clarify in the coming weeks whether or not the cases currently pending meet this high bar.

In a pending appeal, attorneys for Alabama death row inmate Joseph Smith are fighting his conviction on the grounds that he should be considered mentally disabled. A series of tests showed Smith’s IQ was just over 70, a threshold cited in a previous Supreme Court decision.

But the 11th U.S. Circuit Court of Appeals said the number was not a strict cut-off and that variations in testing could cause his actual IQ to be slightly below 70. Alabama is appealing that decision to the Supreme Court and has been waiting for a response for more than a year.

In Oklahoma, Brenda Andrew faces the death penalty for the 2001 shooting death of her estranged husband. In her appeal to the Supreme Court, Andrew said prosecutors’ use of a “clearly irrelevant sexual history” should throw out her conviction.

“By stripping Ms. Andrew of her humanity as a whole person, the state instead presented to the jury the archetype of a ‘slut’ and a depraved adulterer,” her attorneys told the Supreme Court.

Oklahoma officials responded that the evidence “indicated that Andrew hated her husband and she made no secret of her desire to see him dead.”

CNN’s Devan Cole contributed to this report.

For more CNN news and newsletters, create an account at CNN.com