Samuel J. Bailey, 36, left the Los Angeles County Jail early Wednesday, the Sheriff's Department reported.
In all, 10 convictions have been overturned and charges in one case have been dismissed since the scandal involving officers in the LAPD's Rampart Division broke. More than a dozen officers have been relieved of duty.
The district attorney's office said as many as 40 more convictions could be overturned.
"Our first priority is, if there are any wrong convictions, to right that immediately," said Sandi Gibbons, a DA spokeswoman.
Former Officer Rafael Perez has been cooperating with prosecutors by giving them details of setups and falsified police reports and testimony in exchange for a lighter sentence. He was convicted of stealing cocaine from a police evidence room.
Bailey was jailed in 1996 on a parole violation after pleading guilty to being a felon in possession of a firearm.
Superior Court Judge Larry P. Fidler overturned his plea and two other convictions at the request of county prosecutors. The prosecutors believe officers wrote a phony police report and gave false testimony at Bailey's trial, said his public defender, Francis Bennett.
"There's been a move to bowl (suspects) over in the war on crime," Bennett said.
Also overturned was the conviction of Oscar Peralta for a 1996 shooting in which officers killed one man and wounded two others.
Peralta, who was shot after he allegedly pulled a gun on police, was falsely convicted of assault, prosecutors said. He remains in prison on an unrelated charge of attempted murder.
The third case involved Roy A. Montes, 21, who pleaded guilty in 1996 to possession with intent to sell crack cocaine and attempting to steal a bicycle from an undercover police officer. Montes also remained in prison on a separate conviction.