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Marcellus Williams, the Missouri death row inmate who has maintained his innocence for nearly 24 years, is scheduled to be executed Tuesday, a day after the state’s governor and Supreme Court refused to intervene.

Williams, 55, was convicted of killing former newspaper reporter Felicia Gayle, who was found stabbed to death in her home in 1998, but he has long maintained his innocence.

Unless the U.S. Supreme Court intervenes, he is scheduled to be executed by lethal injection at Bonne Terre State Prison on Tuesday at 6 p.m. CT.

The case raises the possibility that an innocent person will be executed, a risk that comes with the death penalty. At least 200 people sentenced to death since 1973 have later been acquitted, four of them in Missouri, according to the Death Penalty Information Center.

The NAACP and the Council on American-Islamic Relations have called on Governor Mike Parson to stop Williams’ execution.

Over the weekend, Williams’ attorneys and St. Louis County District Attorney Wesley Bell filed a joint brief asking the state Supreme Court to remand the case to a lower court for a “more comprehensive hearing” on Bell’s January motion to overturn Williams’ 2001 conviction and sentence.

The St. Louis District Attorney’s Office, which tried Williams in 2001, argued in its motion in January that DNA testing of the murder weapon could rule out Williams as Gayle’s killer. But that argument fell apart at a district court hearing last month when new DNA testing that identified the murder weapon was mishandled, tainting evidence meant to exonerate Williams and complicating his attempt to prove his innocence.

And at Monday’s hearing, the Missouri Supreme Court refused to stop Williams’ execution.

Ultimately, the state Supreme Court unanimously decided not to stay the execution because the prosecutor “failed to establish by clear and convincing evidence Williams’ actual innocence or a constitutional error in the original criminal trial that undermines confidence in the verdict of the original criminal trial,” the opinion said. The opinion also said, “Because this Court denies this appeal on the merits, the motion to stay the execution is denied as moot.”

“Mr. Williams has exhausted all legal avenues and has gone through over 15 hearings to prove his innocence and overturn his conviction,” Parson said in a statement following the decision.

“No jury or court, at the trial, appellate, or Supreme Court level, has ever found Mr. Williams’ claims of innocence to be justified. Ultimately, his conviction and death sentence were affirmed. None of the actual facts of this case led me to believe in Mr. Williams’ innocence, so Mr. Williams’ punishment will be carried out as ordered by the Supreme Court.”

During Monday’s hearing, Williams’ attorney Jonathan Potts claimed that a prosecutor had struck a juror from the jury pool during his trial “because, among other things, he was a young black man with glasses.”

“There was also a racist component to it,” Potts said.

However, the Missouri Attorney General’s office disputed this view, arguing that the prosecutor’s intent to reject the potential juror was not based on race.

Tricia Rojo Bushnell, an attorney for Williams, said in a statement after the decision on Monday that the “courts must intervene to prevent this irreparable injustice.”

“Missouri is on the verge of executing an innocent man, an outcome that calls into question the legitimacy of the entire criminal justice system,” she said.

In his own statement Monday, Bell said he and other attorneys would continue the fight to save Williams’ life.

“Even for those who oppose the death penalty, irreversible execution should not be an option when there is even the slightest doubt about the defendant’s guilt,” Bell said.

On September 18, less than a week before the scheduled execution, Williams’ team filed a petition for clemency with the U.S. Supreme Court.

In the petition, Williams’ lawyers argued that he was denied his right to due process during the years-long legal battle to save his life.

They pointed out that former Missouri Governor Eric Greitens had previously stayed Williams’ execution indefinitely and set up a commission to investigate his case and decide whether he should be granted clemency.

“The panel investigated Williams’ case for the next six years – until Governor Michael Parson abruptly ended the proceedings,” the lawyers wrote.

When Parson took office, he dissolved the board and revoked Williams’ stay of execution, the petition says. Parson’s decision denied Williams his right to due process, Williams’ lawyers argued.

“The Governor’s actions violated Williams’ constitutional rights and required the Court’s attention with extraordinary urgency,” the court documents say.

Just one day before the scheduled execution, Williams’ team also asked the U.S. Supreme Court to stay the execution because they believed there was evidence of racial bias in the selection of the jury.

In the case, Bell, who took office in 2018 and is now running for Congress as a Democrat, faced Republican Attorney General Andrew Bailey, who is seeking re-election. Bailey had fought Bell’s January motion, arguing that new DNA test results suggested the evidence did not exonerate Williams.

Last month, Bell’s office announced it had reached a settlement with Williams. Under the settlement, which was approved by the court and Gayle’s family, the inmate would have entered an Alford guilty plea to first-degree murder and received a life sentence.

But the state’s attorney general opposed the deal and appealed to the state Supreme Court, which blocked the agreement.

CNN’s Dakin Andone and Lauren Mascarenhas contributed to this report.