The gunshot that left a rookie Philadelphia cop crippled 45 years ago continues to echo through the city's criminal-justice system.

But it's the man who fired the bullet - and who remains behind bars, despite having served his entire prison sentence - who now seeks a measure of justice.

William Barnes' recent appeal to the federal courts to be released from prison may not win much public sympathy for the 76-year-old inmate. It was Barnes' weapon, fired during a 1966 burglary, that paralyzed Police Officer Walter Barclay.

Barclay lived another 41 years. Yet, city prosecutors tried to turn his 2007 death from an infection into a murder case against Barnes - on the ground that the ex-cop's medical problems stemmed directly from the shooting.

Barnes had paid the debt society demanded of him by completing a 16-year prison sentence for the shooting. He was jailed again, though, in 2007 over the flimsiest of parole violations - carrying a cellphone and car keys without the approval of his parole officer.

But for the parole violations, Barnes should have been out on bail pending his trial on murder charges lodged by then-District Attorney Lynne M. Abraham. He posed no threat at his advanced age.

He poses even less threat today, having been acquitted of the tenuous murder charge by a city jury in May 2010. Still, Barnes remains in jail, denied parole four times since his murder acquittal. This over an original six-month sentence for the parole infraction.

Barnes' continued incarceration appears to be driven by sour-grapes objections from District Attorney Seth Williams' office, which was unable to get the murder conviction it sought. Prosecutor Ed Cameron called Barnes a "vile criminal" who "should spend the rest of his life in prison."

Prosecutors don't get to be judge, jury, and jailer, though - especially since Barnes was exonerated in Barclay's death. It should be obvious to a federal judge that Barnes' rights are being violated. It's time to end an imprisonment that serves only as spiteful revenge.