The Bay Area transit officer charged with murdering an unarmed man has been freed on $3 million bail.

Alameda County Sheriff's Sgt. J.D. Nelson said Johannes Mehserle posted bail around 3:45 p.m. Friday at Santa Rita Jail in Dublin. 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 said Mehserle shot 22-year-old Oscar Grant in the back while the man lay facedown on the ground. But the defense said he may have mistakenly pulled his pistol instead of a stun gun.

The shooting, caught on cell phone videos, has sparked numerous protests against the former officer, whose family has reported death threats. Protesters outside Mehserle's bail hearing last week demanded that he remain jailed.