ROCHESTER, Minn. — Donald Williams, who witnessed George Floyd's death and whose testimony could be critical in the murder trial of Derek Chauvin, will be allowed to use his mixed martial arts experience and knowledge if called to testify.

Williams, wearing a black "Northside Boxing Club" sweatshirt, was among those who pleaded with police on May 25, 2020, as Chauvin pressed his knee on Floyd's back while three other Minneapolis officers stood by.

"He is not even resisting arrest," Williams said to the police, according to one of the police body cam videos. "You think that's cool? What's your badge number? You're a bum for that. You're a bum for that, bro. He's not responsive right now. You call what he's doing OK?"

Williams lived in Rochester, Minn., for nearly two years as a Rochester Community and Technical College student and wrestler in 2007 and 2008, a Rochester Community college official confirmed.

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In a brief interview with Forum News Service, Williams said he could not discuss the case or the role he might play as a witness in the case.

"It's something I won't go into," he said.

Williams said he came to Rochester to wrestle, but his life ended up taking a detour. After he left Rochester, he went into martial arts and trained as an MMA fighter.

"Things didn't go as planned because of my kid, but I chose a different route and ended up going into martial arts and becoming an amateur and pro fighter," Williams said.

In an interview with CNN after Floyd's death, Williams looked visibly distraught as he described what happened.

"They wanted to kill that man," he told host Chris Cuomo last summer. "I seen it in his eyes. I seen it in his demeanor. He had no feeling. He had no remorse."

WATCH: Donald Williams' emotional interview with Chris Cuomo on CNN

Earlier this week, Chauvin's defense attorney, Eric Nelson, tried to limit what Williams could testify about in court. The defense did not seek to hinder Williams from speaking about what he saw that day, but they did not want him to share his opinion regarding mixed martial arts holds and techniques.

The defense argued that his "training, experience and/or expertise in mixed martial arts, boxing or other training on the grounds that it is irrelevant and overly prejudicial."

On Wednesday, March 10, Judge Peter Cahill ruled that Williams, one of the most vocal people in the group urging police to relent in their handling of Floyd, can testify about his mixed marital arts training and experience. The judge said that Williams would be permitted to touch on matters relating to the use of "blood chokes."

State prosecutor Matthew Frank said that Williams has been wrestling since he was 13 and that he has fought nearly 20 times. Williams trained alongside officers from various Minneapolis-area police departments.

Known as "The Deathwish," Williams had a 6-6 record during a fighting career that spanned from 2011 to 2019, according to Tapology. In 2016, he won the Savage Entertainment MMA bantam-weight title.

The judge recently allowed prosecutors to add a charge of third-degree murder against Chauvin, in addition to the more serious charge of one count of second-degree murder.