CHICAGO (AP) — A former Illinois death row inmate whose exoneration became an incentive to end the death penalty in Illinois has died. Attorney Jim Montgomery says Anthony Porter died this week at age 66.

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.

Porter’s case helped lead former Gov. George Ryan to declare a moratorium on executions in 2003 and to commute the death sentences of more than 150 inmates to life in prison. The death penalty in Illinois was abolished in 2011.