The former Bay Area transit officer charged with murdering an unarmed man was released Friday after posting $3 million bail, authorities said.

Johannes Mehserle, 27, was picked up by a bail bondsman at Santa Rita Jail in Dublin around 3:45 p.m., according to Alameda County Sheriff's Sgt. J.D. Nelson. He had been in custody since his Jan. 13 arrest.

Mehserle has pleaded not guilty to one count of murder in the New Year's Day shooting on a train platform at Oakland's Fruitvale station.

Prosecutors say the Bay Area Rapid Transit officer shot 22-year-old Oscar Grant in the back while the man lay facedown and restrained on the ground. But the defense says he may have mistakenly pulled his pistol instead of a stun gun.

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The shooting, caught on cell phone cameras and broadcast on TV and the Internet, has sparked numerous protests against Mehserle, including several that resulted in arrests for arson and vandalism. Protesters outside Mehserle's bail hearing last week demanded that he remain jailed.

Mehserle's family also has reported death threats and say they've been forced to leave their homes.

On Friday, about 150 protesters already were gathered outside Oakland's City Hall for a demonstration when news broke of Mehserle's release. Oakland police spokesman Jeff Thomason said extra officers were put on the street as a precaution, but the crowd had begun dispersing by evening.

Oakland Mayor Ron Dellums called on protesters to remain peaceful.

"We must treat each other and our city with respect and dignity while the outcome of this case is determined by judge and jury," he said in a statement.

John Burris, who is representing Grant's family in a $25 million wrongful death claim against BART, also urged calm.

"We hope the public will not create any social unrest as a consequence of this," Burris said. The family wants peace and the process to flow in the normal course of events."

Oakland resident Javier Reyes, 44, who was at Friday's protest, said Mehserle's release was "a slap to the citizens of Oakland."

"I know he should be in prison," Reyes added.

Morna Campbell, 53, objected to the judge's decision to set bail. "He doesn't deserve bail because he's already proved he's a flight risk," she said. "They should keep him in jail because he's a threat to the public and himself."

At the Jan. 30 bail hearing, Judge Morris Jacobson said he set the high amount in part because he considered Mehserle a flight risk after the former officer fled to Nevada during the initial investigation.

As a condition of release, Mehserle was ordered to surrender all weapons. He has turned over a .45-caliber Glock semiautomatic pistol and a .40-caliber semiautomatic pistol to another party, according to documents filed Friday.

It's unclear where Mehserle was headed after posting bail. His attorney, Michael Rains, did not immediately return a call, and the judge has imposed a temporary gag order in the case until the next hearing, on Feb. 13.