LOS ANGELES (AP) — An unarmed black man killed by a transit police officer on a train platform near San Francisco last year was scared of being shot with a Taser stun gun, harkening back to a prior run-in with police that led to his arrest.

Carlos Reyes, who testified about shooting victim Oscar Grant on Monday, fought back tears as he watched a video of himself sitting several feet away from where Grant was shot in the back.

It was the second time in three days in which a friend of Grant was overcome by emotion during testimony at the trial of former Bay Area Rapid Transit officer Johannes Mehserle, who has pleaded not guilty to murder.

The case has stirred racial tensions — Grant, 22, was black and the 28-year-old Mehserle is white.

Mehserle was among several BART officers who were called when Grant became involved in an altercation aboard the train that arrived at Oakland's Fruitvale station on New Year's Day 2009.

On Monday, Reyes viewed one of the videos and said he looked away for a second when he heard the gunshot that killed Grant as he was lying face down

"I kept telling him it was going to be OK," Reyes recalls telling Grant. "I told him, 'Keep your eyes open.'"

Reyes, 22, testified he heard Mehserle say moments after the shooting, "'Oh (expletive), I shot him.'" Mehserle resigned shortly after the shooting.

Last week, Jamil Dewar turned away from a large television screen and began crying after hearing the gunshot. Dewar, 17, was consoled by his mother who ran to him while he was on the witness stand.

Other people who saw the events leading up to the shooting also said they were deeply affected. Lydia Clay, who was with three friends on the train, said she was "upset and angry" that Grant had been shot.

"Because it should have never happened," Clay said.

Defense attorney Michael Rains has maintained that Mehserle meant to pull out his Taser stun gun instead of his .40-caliber handgun when he shot Grant. In his opening statements, Rains said Mehserle told fellow BART officer Tony Pirone before the shooting, "Tony, Tony, Tony, I can't get his hands. I'm going to tase him."

Pirone was fired in April.

Prosecutors believe Mehserle did intend to shoot Grant and that he used his weapon because officers were losing control of the situation.