Three cases are pending before the U.S. Supreme Court with only hours remaining before Marcellus Williams is scheduled to be executed in Missouri.

Williams’ death warrant goes into effect at 6 p.m. Tuesday.

The 55-year-old was convicted in the 1998 murder of Felicia Gayle in the St. Louis area. He has maintained that he is innocent and that no forensic evidence ties him to the crime.

On Monday, Gov. Mike Parson denied clemency. The Missouri Supreme Court denied an appeal brought by St. Louis County Prosecutor Wesley Bell, who supports vacating Williams’ conviction.

The three questions before the U.S. Supreme Court are Williams’ last chances at avoiding death. One of them asks whether reversal is necessary when “a capital conviction is so infected with errors that the prosecutor who prosecuted the case no longer seeks to defend it.” It was brought late Monday after the Missouri Supreme Court rejected Bell’s appeal.

The other cases argue that the trial prosecutor struck a potential juror from the pool because he was Black and question whether capital defendants have due process rights in the clemency process.

Bell initially intervened on behalf of Williams in January.

Though the prosecutor had filed a motion in support of vacating Williams’ conviction, the Missouri Supreme Court in June scheduled the execution for Sept. 24.

A hearing last month in Bell’s motion revealed that recent DNA testing showed the original trial prosecutor’s DNA on the murder weapon. Former prosecutor Keith Larner admitted to handling the knife at least five times without gloves. Potential DNA evidence belonging to the perpetrator could have been removed when the weapon was mishandled. That weakened Williams’ case, and he agreed to plead no contest. The deal would have re-sentenced him to life without parole and spared him from capital punishment. But the Missouri Attorney General’s Office opposed the agreement, and the Missouri Supreme Court struck down the deal.

A full evidentiary hearing then took place before St. Louis County Circuit Judge Bruce Hilton. He ultimately denied Bell’s efforts, narrowing Williams’ chances of avoiding execution.

Two petitions opposing Williams’ execution have garnered more than one million signatures, according to the Innocence Project. The execution is also opposed by Amnesty International, the NAACP, the Council on American-Islamic Relations and Rep. Cori Bush, a St. Louis Democrat.

Gayle’s family has also said they do not want to see the execution carried out.

Williams was primarily convicted on the word of two witnesses who said he had confessed to them. One of them led authorities to his car, where some of Gayle’s belongings were located. Both of those witnesses have since died.