Johannes Mehserle was set free from a Los Angeles County jail after serving 11 months of a two-year sentence. Los Angeles County Superior Court Judge Robert Perry ruled Friday that Mehserle should be given credit for time served and good conduct.
Mehserle, 29, was convicted of involuntary manslaughter last July in the shooting death of Oscar Grant on New Year's Day 2009.
The case captured the nation's attention, and there was so much racial tension over the white officer killing an unarmed black man that the trial had to be moved from the Bay area to Los Angeles.
The former Bay Area Rapid Transit (BART) officer and his partner were responding to an unruly crowd on a BART platform in Oakland. While attempting to subdue Grant, Mehserle fatally shot him. Mehserle testified that he meant to use his stun gun instead of his .40-caliber pistol.
The incident was recorded on tape by bystanders and showed Mehserle firing a bullet into the back of Grant as he lay face down after being pulled off a train for allegedly fighting.
"We're very clear. It wasn't involuntary manslaughter. That was cold-blooded murder," said Pete White of the Los Angeles Community Action Network.
About two dozen demonstrators and members of Grant's family gathered in front of the Los Angeles criminal courts building on Monday to protest the early release.
"We did not receive justice in this whole proceeding. We've been denied our rights," said Cephus Johnson, Grant's uncle.
Protesters marched to the federal courthouse, demanding that the U.S. Attorney General file federal charges against Mehserle.
Johnson read from a letter from Congresswoman Maxine Waters, who also supports a federal investigation into the facts and proceedings surrounding the case.