Executing a Black man in Missouri who says he was wrongfully convicted would amount to a “horrible miscarriage of justice,” the president of the NAACP said in a letter Wednesday calling on the governor to halt the execution planned for next week.

Prosecutors want to vacate the conviction of Marcellus Williams over doubts about evidence in the case, NAACP President Derrick Johnson pointed out in the letter obtained by The Associated Press. Relatives of the woman who was killed also oppose the execution.

Several efforts are underway to spare Williams' life. Attorneys with the Midwest Innocence Project on Wednesday filed an emergency appeal with the U.S. Supreme Court seeking a stay. They’ve also asked a federal court and the Missouri Supreme Court to intervene, and asked Gov. Mike Parson to grant clemency.

None of the physical evidence has linked Williams to the 1998 stabbing death of Lisha Gayle, according to a statement from the St. Louis County Prosecuting Attorney’s Office included in Johnson's letter. Executing Williams would perpetuate a history of racial injustice in the use of the death penalty in Missouri and elsewhere, Johnson wrote. The NAACP is opposed to the death penalty.

“Taking the life of Marcellus Williams would be an unequivocal statement that when a white woman is killed, a Black man must die. And any Black man will do,” Johnson wrote.

Williams, 55, is scheduled to die by injection Tuesday despite an innocence claim strong enough to prompt Missouri's previous governor to grant a last-minute reprieve in 2017. St. Louis County's current prosecutor also was convinced that Williams' murder conviction and death sentence should be thrown out.

Issues of racial bias in Williams' conviction have been raised before.

Williams was convicted of first-degree murder in 2001. The prosecutor in the case, Keith Larner, testified at a hearing last month that the trial jury was fair, even though it included just one Black member on the panel.

Larner said he struck just three potential Black jurors, including one man because he looked too much like Williams. He didn't say why he felt that mattered.

Williams narrowly escaped execution before. In August 2017, hours before his scheduled death, then-Gov. Eric Greitens, a Republican, granted a stay after reviewing DNA evidence that found no trace of Williams' DNA on the knife used to kill Gayle. Greitens appointed a panel of retired judges to examine the case, but that panel never reached any conclusion.

That same DNA evidence prompted Democratic St. Louis County Prosecuting Attorney Wesley Bell to request a hearing challenging Williams’ guilt. But days before the Aug. 21 hearing, new testing showed that the DNA evidence was spoiled because members of the prosecutor’s office touched the knife without gloves before the original trial.

With the DNA evidence unavailable, Midwest Innocence Project attorneys reached a compromise with the prosecutor’s office: Williams would enter a new, no-contest plea to first-degree murder in exchange for a new sentence of life in prison without parole.

Judge Bruce Hilton signed off on the agreement, as did Gayle’s family. But at Republican Attorney General Andrew Bailey’s urging, the Missouri Supreme Court blocked the agreement and ordered Hilton to proceed with an evidentiary hearing.

Hilton ruled on Sept. 12 that the first-degree murder conviction and death sentence would stand.

“Every claim of error Williams has asserted on direct appeal, post-conviction review, and habeas review has been rejected by Missouri’s courts,” Hilton wrote. “There is no basis for a court to find that Williams is innocent, and no court has made such a finding.”

The clemency petition from the Midwest Innocence Project focuses heavily on how Gayle’s relatives want the sentence commuted to life without parole. “The family defines closure as Marcellus being allowed to live,” the petition states.

U.S. Rep. Cori Bush, a St. Louis Democrat, also wrote to Parson urging clemency.

You have it in your power to save a life today by granting clemency to a man who has already unjustly served 24 years in prison for a crime he did not commit," Bush wrote. “We urge you to use it.”

Parson, a Republican and a former county sheriff, has been in office for 11 executions, and has never granted clemency. His spokesman said a decision will likely come at least 24 hours before the scheduled execution.

Prosecutors at Williams’ original trial said he broke into Gayle’s home on Aug. 11, 1998, heard water running in the shower, and found a large butcher knife. When Gayle came downstairs, she was stabbed 43 times. Her purse and her husband’s laptop were stolen.

Authorities said Williams stole a jacket to conceal blood on his shirt. Williams’ girlfriend asked him why he would wear a jacket on a hot day. The girlfriend said she later saw the laptop in the car and that Williams sold it a day or two later.

Prosecutors also cited testimony from Henry Cole, who shared a cell with Williams in 1999 while Williams was jailed on unrelated charges. Cole told prosecutors Williams confessed to the killing and offered details about it.

Williams’ attorneys responded that the girlfriend and Cole were both convicted of felonies and wanted a $10,000 reward.

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Whitehurst reported from Washington, D.C. Salter reported from O'Fallon, Missouri.