Mehserle served two years in prison and was released this summer. He was convicted of involuntary manslaughter last year in the shooting death of Oscar Grant. Mehserle is now one of five defendants in the federal civil rights trial. He was on the stand Wedneday.
Mehserle came to court with his father and the other four defendants who are all still BART officers. Kenneth Carrethers is suing them for using excessive force when they arrested him at the Oakland Coliseum station three years ago.
Carrethers says he's still suffering from the trauma.
"They're not allowed to hit anybody; they're not allowed to beat nobody up," Carrethers said.
Watching the proceedings were the uncle and aunt of Oscar Grant's aunt and uncle. Mehserle shot and killed Grant six weeks later on New Year's Day 2009.
"The thought patterns Johannes Mehserle had needs to be addressed and BART failed to do that with Kenneth Carrethers, thereby allowing him to kill Oscar Grant," Grant's uncle Cephus Johnson said.
"He's a convicted felon, sure he's going to say whatever he wants to say to get him off," Carrethers' attorney Chris Dolan said.
On Nov. 15, 2008, Carrethers says his car was broken into at the BART parking lot and that officers attacked him when he made a remark that police had done nothing about it.
Dolan says Carrethers was hog tied, a restraining procedure banned by BART police.
"A hog tie means you put someone's legs in shackles, you put their arms in shackles and you tie them together like a pig," Dolan said.
But the defendants disputed that claim, saying they used what's called a "hobble restraint," a nylon strap which loops around the leg because Carrethers was kicking as he was being subdued.
Mehserle wrote in his police report Carrethers was "using profanities" and "making verbal threats" against the officers. Mehserle testified Carrethers was confrontational and aggressive.
"He was grabbed because it appeared he was about to hit another officer in the back of the head who was walking away from him," the defendants' lawyer Dale Allen said.
Mehserle's father got into trouble with the judge when he began taking cell phone pictures of Oscar Grant's uncle outside the courtroom just after court adjourned. Security officers confiscated his phone and now the judge is considering sanctions against him.