Mark David Chapman, 45, who stunned the world 20 years ago when he shot and killed John Lennon outside of the musician's New York apartment, will ask a parole board to set him free today. Having been locked away in Attica prison, Chapman is expected to tell the board that he is a born-again Christian who is no longer a threat to society. Lennon's widow, Yoko Ono, has reportedly written to prison officials, requesting that they keep the assassin behind bars, fearing that, if set free, Chapman would stalk her and Lennon's sons, Sean and Julian.