MINNEAPOLIS — A witness who saw then-Minneapolis police Officer Derek Chauvin hold his knee to George Floyd’s neck for more than nine minutes in May 2020 said he called 911 after watching medics load an unresponsive Floyd into an ambulance because he believed that police had murdered the 46-year-old.

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“I did call the police on the police,” Donald Williams, a 33-year-old mixed martial artist, said on the second day of Chauvin’s trial in Minneapolis. “I believe I witnessed a murder. … I didn’t know what else to do but call (911).”

Williams was among several people heard yelling for Chauvin to get off Floyd in viral cellphone footage of the May 25, 2020, confrontation.

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“You could see that (Floyd) was going through tremendous pain and you could see it in his face, from the grunting,” Williams said Tuesday. “You could see his eyes slowly rolling back in his head, and him having his mouth open -- wide open.”

A former wrestler who said he was trained in martial arts, including chokeholds, Williams testified Monday that he thought Chauvin used a shimmying motion several times to increase the pressure on Floyd. He said he watched Floyd “slowly fade away … like a fish in a bag.”

On Tuesday, Williams told jurors that he tried to talk to officers at the scene, but that “we just didn’t have (a) connection. I spoke to them but not on the connection of a human being relationship.” He said that at one point, he tried to get off a sidewalk and onto the street where the incident was happening, but that another officer on the scene, Tou Thao, put his hand to Williams’ chest to stop him.

In a 911 call played in court, Williams reported that an officer “just pretty much killed this guy that wasn’t resisting arrest.”

“The man went limp, stopped breathing. He wasn’t resisting arrest or nothing, he was already in handcuffs -- they pretty much just killed that dude,” Williams said in the 911 call. “I don’t even know if he’s dead for sure, but he was not responsive when the ambulance just came and got him.”

Williams wiped his eyes in court as the 911 recording played.

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In opening arguments Monday, Nelson said Floyd was fighting efforts to put him in a squad car as the crowd of onlookers around Chauvin and his fellow officers grew and became increasingly hostile.

“There’s a growing crowd and what officers perceive to be a threat. They’re called names,” Nelson said. “They’re screaming at them, causing the officers to divert their attention from the care of Mr. Floyd to the threat that was growing in front of them.”

On Tuesday, Williams insisted that he did not get increasingly angry.

“I grew professional and professional,” Williams answered. “I stayed in my body.”

Authorities arrested Chauvin in May 2020 after video surfaced on social media showing him pressing his knee to Floyd’s neck. The Hennepin County medical examiner ruled the death a homicide, determining that Floyd’s heart stopped as he was being restrained. A separate autopsy commissioned for Floyd’s family also called his death a homicide but concluded that he died of asphyxiation due to neck and back compression.

The trial is expected to last about four weeks at the courthouse in downtown Minneapolis, which has been fortified with concrete barriers, fencing, and barbed and razor wire. City and state leaders are determined to prevent a repeat of damaging riots that followed Floyd’s death, and National Guard troops have already been mobilized.

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Floyd’s death prompted global outrage and sparked a national reckoning over racism and police brutality.

Three other officers also face charges in Floyd’s death. Thomas Lane, Thao and J. Alexander Kueng are charged with aiding and abetting second-degree murder and aiding and abetting second-degree manslaughter. They are expected to face juries in August.

The Associated Press contributed to this report.

Cox Media Group