MINNEAPOLIS (NewsNation Now) — The teenager who shot cellphone video of George Floyd under the knee of Minneapolis police officer Derek Chauvin, 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 buy snacks at Cup Foods convenience store with her younger cousin when she came upon the officers.

“I see a man on the ground, and I see a cop kneeling down on him,” Frazier told the jury, explaining why she first made sure her young cousin had safely gone inside the store, out of sight. “A man terrified, scared, begging for his life.”

Frazier lost her composure and grew emotional at times when prosecutors brought up a still from her video, showing the moment when Chauvin, his knee on Floyd’s neck, appears to look directly into Frazier’s camera lens.

“Yes,” she said, crying and catching her breath when asked if she recognized him. “This was the officer that was kneeling on George Floyd’s neck.”

Chauvin’s lawyers have said that Chauvin was distracted from “the care” of Floyd by the angry bystanders that joined Frazier on the sidewalk.

Prosecutors asked her whether she heard any bystanders threaten the police, and she said no.

“Would you describe yourselves as an unruly mob?” Jerry Blackwell, a prosecutor, asked her.

“No,” Frazier said.

Floyd’s death and the video of Floyd pleading for his life and distressed onlookers yelling at Chauvin to get off him sparked sometimes-violent protests worldwide and a reckoning over racism and police brutality in the U.S.

At the scene, 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,” Frazier told the jury.

When asked by a prosecutor whether she saw violence anywhere on the scene, she replied: “Yes, from the cops. From Chauvin, and from officer Thao.”

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.”

“It’s been nights I stayed up, apologizing and apologizing to George Floyd for not doing more, and not physically interacting and not saving his life,” she said, adding of Chauvin: “But it’s like, it’s not what I should’ve done, it’s what he should’ve done.”

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.

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.”

The Associated Press and Reuters contributed to this article. Reporting by Steve Karnowksi/AP, Amy Forliti/AP and Jonathan Allen/Reuters.