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

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

He will be executed by lethal injection at 6 p.m. CT Tuesday at the state prison in Bonne Terre, unless the U.S. Supreme Court intervenes.

The case raises the specter of potentially putting an innocent person to death, an inherent risk of the death penalty. At least 200 people sentenced to death since 1973 have later been exonerated, 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 petition with the state Supreme Court to send the case back to a lower court for a “more extensive hearing” on Bell’s January motion to overturn Williams’ 2001 conviction and sentence.

The St. Louis District Attorney’s Office, which handled Williams’ 2001 trial, argued in a January motion that DNA testing of the murder weapon could eliminate Williams as Gayle’s killer. But that argument fell apart at a court hearing last month when new DNA testing revealed the murder weapon had been misfired, contaminating evidence that would have exonerated Williams and complicating his quest to prove his innocence.

During Monday’s hearing, the Missouri Supreme Court decided not to stay Williams’ execution.

Ultimately, the state Supreme Court unanimously decided not to halt the execution because the prosecution “failed to establish by clear and convincing evidence Williams’ actual innocence or constitutional wrongdoing at the original trial, which undermines confidence in the original trial’s verdict,” the opinion said. The opinion also stated that “because this Court dismisses this appeal on the merits, the motion for a stay of execution is dismissed as irrelevant.”

“Mr. Williams has exhausted due process and all legal remedies, including more than 15 hearings attempting to prove his innocence and overturn his conviction,” Parson said in a statement after the decision.

“No jury or court, including at the trial, appellate, and Supreme Court levels, has ever found Mr. Williams’ claims of innocence valid. Ultimately, his conviction and death sentence were upheld. Nothing in the actual facts of this case has led me to believe in Mr. Williams’ innocence, and as such, Mr. Williams’ sentence will be carried out as ordered by the Supreme Court.”

During Monday’s hearing, Williams’ attorney Jonathan Potts alleged that a prosecutor during his trial omitted a juror from the jury pool “in part because he was a young black man with glasses.”

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

The Missouri Attorney General’s Office disputed this idea, stating that it was not the prosecutor’s intent to eliminate potential jurors based on race.

In a statement following Monday’s decision, Tricia Rojo Bushnell, an attorney for Williams, said 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.

Bell said in his own statement Monday that he and other advocates will continue the fight to save Williams’ life.

“Even for those who disagree with the death penalty, the irreversible punishment of execution should not be an option if there is even a shadow of doubt about a 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’ attorneys argued that he was denied his right to a fair trial during the years-long legal battle to save his life.

They noted that former Missouri Governor Eric Greitens had previously stayed Williams’ execution indefinitely and formed a commission to review his case and determine whether he should be pardoned.

“The board investigated Williams’ case for the next six years, until Governor Michael Parson abruptly ended the process,” the attorneys wrote.

When Parson took office, he dissolved the board and revoked Williams’ stay of execution, the petition noted. Parson’s decision deprived Williams of his right to a fair trial, Williams’ attorneys argued.

“The Governor’s actions violated Williams’ constitutional rights and created an exceptionally urgent need for the Court’s attention,” the court documents said.

Just one day before the scheduled execution, Williams’ team asked the U.S. Supreme Court to stay the execution, based on what they saw as evidence of racial bias in jury selection.

The case pitted Bell, who took office in 2018 and is now running for Congress as a Democrat, against Republican Attorney General Andrew Bailey, who is seeking re-election. Bailey had opposed Bell’s January motion, saying new DNA test results showed the evidence did not exonerate Williams.

Last month, Bell’s office announced it had reached a plea agreement with Williams. Under the sentence, approved by the court and Gayle’s family, the inmate would have entered an Alford plea to first-degree murder and been resentenced to life in prison.

But the state attorney general’s office 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.