The former Minneapolis police officer who was convicted of murdering George Floyd is seeking to overturn his federal civil rights conviction.

Derek Chauvin, who is serving a 21-year sentence at a federal prison in Arizona, filed a motion to vacate his conviction on Monday (Nov. 13), alleging that has new evidence that shows he did not cause Floyd’s death, the Minneapolis Star Tribune reports.

Chauvin claims in the motion that his trial attorney, Eric Nelson, failed to inform him that Kansas-based pathologist Dr. William Schaetzel offered to testify about his cause of death theory. 

The ex-officer said he would not have pleaded guilty to the federal charges in 2021 if he knew about Schaetzel.

The Associated Press reports that Chauvin’s motion asks the court to throw out his conviction and order a new trial, or at least an evidentiary hearing.

A viral video showed Chauvin kneeling on the handcuffed Floyd’s neck for more than nine minutes, ignoring his plea to be allowed to breathe. The fatal May 2020 arrest ignited nationwide racial justice protests.

At Chauvin’s state trial, the jury heard testimony from the county medical examiner’s office that Floyd’s death was a homicide stemming from cardiac arrest likely caused by the restraint. Chauvin’s defense team argued that Floyd died of natural causes related to his drug use.

An independent autopsy by a doctor for Floyd’s family found that he died of asphyxia due to sustained forceful pressure.

But Schaetzel concluded that Floyd did not die of asphyxia during his encounter with Chauvin but from a rare tumor called a paraganglioma that can cause a fatal surge of adrenaline.

“I can’t go to my grave with what I know,” Schaetzel, who based his findings on his review of autopsy reports, told the AP.

According to Chauvin’s motion, Schaetzel contacted Nelson in April 2021 to say he was willing to testify, but Nelson ignored the offer and didn’t tell Chauvin.

Chauvin waived his rights to appeal his federal conviction except for a claim of ineffective counsel. The AP and Star Tribune asked Nelson for a comment, but he declined.

In a separate state conviction, a jury in 2021 found Chauvin guilty of second-degree unintentional murder, third-degree murder and second-degree manslaughter. The judge sentenced Chauvin to serve more than 22 years in prison.