William Barnes has been behind bars since the August 2007 death of Officer Walter Barclay.
Barnes shot and paralyzed the officer 41 years earlier during a botched burglary. Barnes served 16 years for the shooting but was rearrested and charged with murder after the officer died.
Although a jury acquitted Barnes in May 2010, he remained at Graterford State Prison and was repeatedly denied parole.
Barnes' lawyers took the case to federal court. Then this week, the parole board decided to release Barnes.
His lawyer said Barnes was picked up at the prison mid-day Friday by a friend. He didn't say where Barnes will be living.