The teenager who shot the harrowing video of George Floyd under the knee of the Minneapolis police officer now charged in his death testified Tuesday that she began recording because "it wasn't right, he was suffering, he was in pain."

Darnella Frazier, 18, said she was walking to a convenience store with her younger cousin when she came upon the officers, and sent the girl into the store because she didn't want her to see "a man terrified, scared, begging for his life."

Frazier grew emotional at times, breathing heavily and crying as she viewed pictures of officer Derek Chauvin  kneeling on Floyd last May.

Floyd's death and the video of Floyd pleading for his life and onlookers angrily yelling at Chauvin to get off him triggered sometimes-violent protests around the world and a reckoning over racism and police brutality in the U.S.

One of the bystanders, who identified herself as a Minneapolis firefighter, pleaded repeatedly with officers to check Floyd's pulse, but Chauvin continued to kneel on Floyd's neck, and he and fellow officer Tou Thao wouldn't let onlookers get close, Frazier said.

"They definitely put their hands on the Mace and we all pulled back," she told the jury.

Frazier said of Chauvin: "He just stared at us, looked at us. He had like this cold look, heartless. He didn't care. It seemed as if he didn't care what we were saying."

Chauvin attorney Eric Nelson sought to show that Chauvin and his fellow officers found themselves in an increasingly tense and distracting situation, with the growing crowd of onlookers becoming agitated and menacing over Floyd's treatment.

But when Frazier was asked by a prosecutor whether she saw violence anywhere on the scene, she replied: "Yes, from the cops. From Chauvin, and from officer Thao."

When asked to identify the officer, Chauvin stood up in the courtroom and took off his mask, appearing somber as he looked down and away before putting his mask on.

Earlier Tuesday, a man who was among the onlookers shouting at Chauvin to get off Floyd testified that he called 911 after paramedics took Floyd away, "because I believed I witnessed a murder."

Donald Williams, a former wrestler who said he was trained in mixed martial arts, including chokeholds, returned to the witness stand a day after describing seeing Floyd struggle for air and his eyes roll back into his head. He said he watched Floyd "slowly fade away ... like a fish in a bag."

On Tuesday, prosecutors played back Williams' 911 call, on which he is heard identifying Chauvin by his badge number and telling the dispatcher that Chauvin had been keeping his knee on Floyd's neck despite warnings that Floyd's life was in danger. She offers to switch him to a sergeant.

As he is being switched, Williams can he heard yelling at the officers, "Y'all is murderers, bro!"

During cross-examination, Chauvin attorney Eric Nelson pointed out that Williams seemed to grow increasingly angry at police on the scene, swearing at and taunting Chauvin with "tough guy," "bum" and other names, then calling Chauvin expletives, which the defense lawyer repeated in court.

Williams initially admitted he was getting angrier, but then backtracked and said he was controlled and professional and was pleading for Floyd's life but wasn't being heard.

Williams said he was stepping on and off the curb, and at one point, Thao, who was controlling the crowd, put his hand on Williams' chest. Williams admitted under questioning that he told Thao he would beat the officers if Thao touched him again.

Williams was among the first witnesses as Chauvin, 45, went on trial on charges of murder and manslaughter in Floyd's death.

Prosecutors led off their case by playing part of the bystander video of Floyd's arrest. Chauvin and three other officers were fired soon after the footage became public.

Prosecutor Jerry Blackwell showed the jurors the video after telling them that the number to remember was 9 minutes, 29 seconds  — the amount of time Chauvin  had Floyd pinned to the pavement "until the very life was squeezed out of him."

Nelson countered by arguing: "Derek Chauvin did exactly what he had been trained to do over his 19-year career."

The defense attorney also disputed that Chauvin was to blame for Floyd's death, as prosecutors contend.

Floyd, 46, had none of the telltale signs of asphyxiation and had fentanyl and methamphetamine in his system, Nelson said. He said Floyd's drug use, combined with his heart disease, high blood pressure and the adrenaline flowing through his body, caused a heart rhythm disturbance that killed him.