CHICAGO (AP) — A former Illinois death row inmate whose exoneration became an incentive to end the death penalty in the state has died, his attorney announced Wednesday.

Attorney Jim Montgomery told WBBM Radio that Anthony Porter, 66, died this week. The Cook County Medical Examiner’s Office said Porter died from “anoxic brain injury, probable opioid toxicity,” and ruled the death an accident.

Porter was exonerated in 1999 and released from prison after another man confessed to the Aug. 15, 1982 fatal shooting of two people as they sat in a park on Chicago’s South Side.

Alstory Simon confessed to the crime during an investigation of the murders by a team of journalism students from Northwestern University. Simon was later convicted and sentenced to 37 years in prison.

The Cook County State’s Attorney’s Office re-examined Simon’s conviction in 2013 after he recanted his confession. Simon alleged he was coerced into making it by a private investigator, working with the journalism students, who he says promised him he would get an early release and a share of the profits from book and movie deals.

In 2014, State’s Attorney Anita Alvarez noted the investigation of the case was corrupted and her office could no longer maintain the legitimacy of Simon’s conviction. Alvarez would not say if she believed Simon was innocent.

Simon was released from prison in October, 2014.

Porter’s 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. Illinois, led by Gov. Pat Quinn, abolished the death penalty in 2011.

Porter was arrested in 2011 for stealing deodorant from a Chicago pharmacy. He pleaded guilty to retail theft and was sentenced in 2012 to one year in prison.