A Cook County judge ordered the immediate release Thursday of a prisoner whose confession had helped free a death row inmate in a 1982 double killing.

Alstory Simon's confession in the high-profile case led to the 1999 release of Anthony Porter, who had spent 16 years on death row and whose supporters maintained he was wrongfully convicted. The case was instrumental in the campaign to end Illinois' death penalty, which was abolished in 2011.

Simon was convicted and sentenced to 37 years in prison. But the Cook County State's Attorney's Office began re-examining Simon's conviction last year after he recanted his confession. Simon alleged he was coerced into making it by a private investigator who he says promised him he would get an early release and a share of the profits from book and movie deals.

Cook County State's Attorney Anita Alvarez planned a news conference later Thursday to explain the findings.

At the morning hearing, prosecutors asked the judge to free Simon, and the judge vacated the sentence and conviction. Simon was expected to be freed from Jacksonville prison later Thursday.

The Porter case played a key part in the drive to end the death penalty in Illinois. The case helped lead former Gov. George Ryan to halt all executions in Illinois. Ryan declared a moratorium on executions in 2003 and cleared death row by commuting the death sentences of more than 150 inmates to life in prison. Gov. Pat Quinn abolished the death penalty in 2011.