Prosecutors used amateur video to convince jurors that former Bay Area Rapid Transit Officer Mehserle resorted to deadly force when it was not necessary.
Wanda Johnson said her 22-year-old son was killed in cold blood on New Year's Day 2009. Grant was detained by BART police officers after a disturbance on one of the train platforms.
"I entrusted on my son to get on BART, thinking that he would be okay on BART," Johnson said. "Never did I expect to get a call in the morning to say that my son had been shot."
In his opening statements Thursday, Deputy District Attorney Dave Stine said that Mehserle, 28, let emotions take over his judgment, and that he should be held accountable for his actions. Mehserle did not react to the video tape.
Defense attorney Michael Rains has long contended his client accidentally pulled out a handgun instead of his stun gun. Rains said that there already was a commotion by the time Mehserle responded to a fight that purportedly included Grant and his friends aboard the train.
Rains claims Grant hit BART officer Tony Pirone, who has been described by some witnesses as the most aggressive officer prior to the shooting. Pirone, who does not face criminal charges and is no longer a transit officer, also is heard on one of the tapes using a racial epithet.
Rains added that Mehserle tried to subdue Grant for 12 seconds and that he and Pirone yelled at Grant to "give us your hands." Rains said his client noticed Grant's hands weren't coming out from underneath his stomach.
Outside of the Los Angeles Superior Court, activists who traveled to Los Angeles from the Bay Area promised to keep a close eye on the trial.
"This isn't just for Oscar," said Aidge Patterson, an activist. "This is for everybody who has ever been killed by the police and the police got away with it."
The family and activist have also expressed concern that no one on the jury of eight women and four men is black.
The trial, which was moved from Oakland to Los Angeles due to extensive media coverage, is expected to last about a month.
The Associated Press contributed to this report
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