John Lennon's assassin Mark David Chapman insists "nothing could have stopped" him murdering the former BEATLE.

Chapman gunned Lennon down outside the Dakota Building in New York City in 1980, and claims his mission to kill the IMAGINE singer was triggered when he looked at THE Beatles' SGT PEPPER'S LONELY HEARTS CLUB BAND album cover in his Hawaiian home.

And, as his animosity towards Lennon's success grew, Chapman knew he would not be satisfied until Lennon was dead.

He says, "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.

"Something in me just broke. I was under total compulsion. It was like a train, a runaway train, there was no stopping it."

When Chapman finally had the opportunity to assassinate Lennon, he insists a voice in his head urged him to commit the crime which left the world in mourning.

He says, "I heard a voice in my head saying, 'Do it, do it.' And as he passed me I pulled out the gun, aimed at his back and pulled the trigger five times in succession."

Chapman, now 50, has been refused parole three times at the request of Lennon's widow YOKO ONO - but he is eligible for release again next year (06).