She had walked to Cup Foods hundreds of times before May 25, 2020.
That day, Darnella Frazier made a phone video that convulsed a nation: a recording of a white policeman kneeling on the neck of George Floyd, a black man dying in handcuffs on a Minneapolis street.
Ten months later, the 18-year-old once again found herself up close to Derek Chauvin, whose face she made recognisable around the world.
On Tuesday, Frazier testified at Chauvin's murder and manslaughter trial. He has said he is not guilty.
Frazier, who suffers social anxiety and since Floyd's death has declined all interview requests, testified that the sight of Floyd on the ground compelled her to stay: "It wasn't right. He was suffering. He was in pain."
Chauvin, 45, and three other policemen arrested Floyd on suspicion he had used a fake $20 bill to buy cigarettes at Cup Foods. Frazier, who grew up in the neighbourhood, arrived a few minutes later.
The nearly 10-minute video she made and posted to her Facebook page catalysed the largest protest movement seen in decades in the United States, filling streets in cities across the country with demonstrations against racism and police brutality against black people.
Protests also ignited outside the United States.
Frazier cried when prosecutors showed her a frame of her video, a moment when Chauvin, his knee on Floyd's neck, appears to look directly into her lens.
"He had this cold look, heartless," Frazier said, as Chauvin listened at a nearby table, taking notes in a yellow legal pad.
"He didn't care what we were saying, it didn't change anything he was doing."
In December, the video earned Frazier the 2020 Benenson Courage Award from PEN America, presented to her by the filmmaker Spike Lee.
"It's just a lot to take in," she said in an acceptance speech she recorded at her home.
She offered a rare comment on Chauvin in a post to her Facebook page on March 11, a few days after the trial began with jury selection: "That man was begging for his life and Chauvin did not care," she said.
"He deserves to go down."
Chauvin's lawyers say he was following the training he had received in his 19-year career as policeman.
The day after Floyd died, the Minneapolis Police Department fired Chauvin.
Seth Cobin, a lawyer representing Frazier, said on Tuesday she was under a court order preventing her from giving interviews during the trial.
In court on Tuesday, Frazier told the jury she was walking to Cup Foods with her 9-year-old cousin to buy snacks when she saw "a man terrified, scared, begging for his life".
Chauvin's lawyers have said Chauvin was distracted from "the care" of Floyd by angry bystanders.
Prosecutors asked Frazier whether she heard any bystanders threaten the police. She said no.
"Would you describe yourselves as an unruly mob?" Jerry Blackwell, a prosecutor, asked.
Frazier said the only person she saw being violent was Chauvin.
She was asked by both sides how producing the famous record of Floyd's death had changed her life.
She answered through tears that she did not wipe away, saying she would sometimes stay up late at night thinking of Floyd and apologising to him for "not saving his life".
"It's not what I should have done. It's what he should have done," she said, referring to Chauvin.