In Missouri, 55-year-old death row inmate Marcellus Williams is scheduled to be executed on Tuesday evening – despite pleas from prosecutors and even his victim’s family.

Missouri Governor Mike Parson and his Supreme Court said Monday that there was enough evidence to kill Williams for the 1998 stabbing murder of Felicia Gayle, a social worker and former reporter with the St. Louis Post-Dispatch.

The state's decision to move forward with the execution is one of the most controversial in recent years. The same prosecutors who convicted Williams are now raising the alarm that he may actually be innocent.

Gayle's family has even called for a pardon, suggesting that life imprisonment without parole would be an appropriate punishment for Williams under the circumstances.

Williams has insisted for decades that he did not, as prosecutors claim, enter Gayle's home on August 6, 1998, stab her 43 times with a butcher knife and then steal her purse and her husband's laptop.

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Investigators recorded fingerprints, footprints, hair and DNA on a kitchen knife at the crime scene, but the investigation lasted more than a year before police arrested Williams. During a trial, it emerged that Williams' DNA did not match forensic evidence recovered from the crime scene.

Nevertheless, Williams was convicted of murder in 2001 and sentenced to death after hearing incriminating testimony from his cellmate, who claimed he confessed to the murder while in prison for another crime. Williams' girlfriend also said she saw the stolen purse and laptop in Williams' car.

Williams' extensive criminal record certainly didn't help him win the jury's favor either. At the time of his conviction, he was serving a 50-year prison sentence for an unrelated robbery.

Still, defense attorneys argued that Williams' former cellmate and his girlfriend were both after the $10,000 reward offered by Gayle's family, and were willing to make up lies if it would benefit them personally. In the end, neither received the payment.

Prison informants are considered particularly problematic. The University of Michigan found that they were involved in 23 percent of all cases in which the death penalty was overturned.

Williams had twice previously avoided execution at the last minute, first by the state Supreme Court in 2015 and then again in 2017 when then-Governor Eric Greitens, a Republican, granted Williams a stay and ordered prosecutors to re-examine the DNA evidence. That DNA evidence may have exonerated Williams, but it was found to have been tampered with by prosecutors' employees who had handled the knife without gloves before the trial.

Now Parson, a former sheriff with 11 years of experience, sits in the governor's mansion in Jefferson City. He has been in office for 11 executions and has never granted clemency.

Parson explained his decision in a statement on Monday, saying: “No jury or court, including at the trial, appellate and Supreme Court levels, has ever found Mr. Williams' claims of innocence to be substantiated.”

The Midwest Innocence Project said it will advocate for Williams' clemency until 6 p.m. CST Tuesday, when he is scheduled to be executed by lethal injection.