Cook County Judge Paul Biebel said the decision was based on DNA evidence recovered from the victim, 30-year-old Nina Glover, the Chicago Tribune reported.
Four men -- who were teenagers at the time of the incident -- were convicted of the slaying. Michael Saunders and Harold Richardson are still serving time, Terrill Swift is out on parole and Vincent Thames served his sentence but must register as a sex offender for the rape conviction.
The DNA belonged to Johnny Douglas, who was convicted of murdering another woman, acquitted of one homicide and a suspect in other murders and sexual assaults. Douglas was shot to death in 2008.
Joshua Tepfer, an attorney at Northwestern University's Center on Wrongful Convictions of Youth, said no DNA evidence linked the four convicted men to the crime and despite their confession, the trial would have ended differently had the judge known Douglas' DNA was found.
Assistant State's Attorney Mark Ertler said there was no way to tell Douglas' DNA was left on Glover at the time of the murder and the evidence was "not significant enough to merit new trials."