It's not just about preventing harm. It's righting a wrong. This guy got away, literally, with murder. He was allowed to live the best years of his life in freedom precisely because he intimidated those that could put him away. There's a chance to rectify that. That the person is now older should have no bearing on whether or not they go to prison, IMO.
"I was thirsty for everything, but blood wasn't my style" - Live, "Voodoo Lady"