John Lennon's killer says nothing could have stopped him from shooting the former Beatle to death in New York 25 years ago.

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Mark David Chapman told a taping of Friday night's "Dateline NBC" he was destined to kill Lennon on Dec. 8, 1980, the New York Post reported Tuesday.

"It was like a train, a runaway train -- there was no stopping it," Chapman said. "Nothing could have stopped me. ... This was a white-knight kind of a thing, a crusade."

In exclusive audiotapes recorded in 1991 and 1992, Chapman said he feared dying a nobody and his identity "would be found in the killing of John Lennon."

He said he was afraid he would die without achieving fame. He chose Lennon because he was his mortal opposite.

"There was a successful man who kind of had the world on a chain, so to speak, and there I was, not even a link of that chain, just a person who had no personality," Chapman said. "And something in me just broke."

Chapman, 50, is serving 20 years to life at New York's Attica state prison.