He could have left. Perhaps something made him decide to stop, but I can't imagine what that would have been. If 1991 was the last murder, then we're talking 14 years ago. Wonder how old his children had gotten by then?
And then, recently, something made him start contacting authorities again....some desire to get caught?...some desire to challenge modern forensics to see if he was still so smart?....something ego driven?....some urge to kill again and he was now rejecting of it?
It's fascinating in a way.