Attorneys for a convicted murderer scheduled to die by lethal injection on Tuesday say the state of Missouri may be preparing to execute an innocent man.

New DNA testing conducted in December could prove the innocence of Marcellus Williams — who was convicted of fatally stabbing a former St. Louis Post-Dispatch reporter during a 1998 robbery – and his attorneys are now seeking a new hearing or a commutation of his sentence to life in prison, the St. Louis Post-Dispatch reports.

The tests show that DNA evidence found on the knife matches an unknown man and not the 48-year-old Williams, according to an analysis by forensic DNA expert and Boise State University biologist Greg Hampikian. Attorney Kent Gipson filed a brief late Monday asking the US Supreme Court to stop the execution and examine the new evidence, including hair samples found on victim Lisha Gayle’s shirt and fingernails that didn’t belong to Williams. A footprint at the scene of the crime also doesn’t match Williams, his attorneys claim.

“In this case, there is conclusive scientific evidence that another man committed this crime,” attorney Kent Gipson wrote in the brief, CNN reports. Supreme Court Justice Neil Gorsuch, meanwhile, has yet to rule on the new motion.

Hampikian said the new evidence isn’t enough to “incriminate someone” but could be used to exclude someone from having committed the grisly murder.

“It’s like finding a Social Security card with some blurred numbers,” he told CNN. “There’s still enough there to at least exclude someone.”

In 2015, the Missouri Supreme Court postponed Williams’ execution to allow for additional DNA testing, but the court denied Williams’ petition last week to halt his execution and either appoint a special master to hear his claims or vacate his death sentence and commute it to life in prison, according to the Dispatch.

But in a statement issued Monday, the state attorney general’s office said Williams was proven guilty by means of other evidence, including a laptop belonging to Gayle’s husband that Williams later sold and two witnesses who say Williams confessed to them.

“Based on the other, non-DNA evidence in this case, our office is confident in Marcellus Williams’ guilt and plans to move forward,” Loree Anee Paradise, deputy chief of staff for Missouri Attorney General Josh Hawley, told CNN in a statement.

Attorneys for Williams have also asked Republican Gov. Eric Greitens for clemency. A spokesman for Greitens told the Post-Dispatch that members of the governor’s staff “will not be able to comment” about the clemency request until Tuesday.

If the execution — scheduled for 7 p.m. ET on Tuesday — goes as planned, Williams’ son said the state will be murdering an “innocent” man, he told CNN.

“He’s at peace,” Marcellus Williams II said. “I think tomorrow he’s going to be murdered. He [is] an innocent man, and that’s not right.”

The younger Williams continued: “Someone murdered that woman, but it wasn’t my father. I wish they would find the right suspect and charge them to the fullest extent of the law.”

Officials at Amnesty International note that Williams, who is black, was convicted of killing Gayle, who was white, by a jury consisting of 11 white jurors and one black juror. The jury also did not hear evidence of Williams prior abuse and mental disability, the group claims.

“The death penalty is abhorrent in any circumstance, and as we have seen time and time again, the capital justice system is capable of error,” Zeke Johnson, senior director of programs at Amnesty International USA, said in a statement. “The state of Missouri must not allow this execution to go forward, and must commute the sentences of all of those on death row. There is no acceptable way for the state to kill its prisoners.”