John Lennon's killer allegedly considered himself a "white knight" on a crusade.
Tapes set to be played on US television this week show Mark Chapman - who shot the legendary Beatle in 1980 - hoped to make his mark by murdering the star.
The 50-year-old, who was filmed form his prison cell, also claimed he couldn't be deterred from his "mission", saying: "Nothing could stop me. This was a white knight kind of thing, a crusade."
Chapman says there was a voice in his head that screamed "do it" three times just before he gunned down the then 40-year-old singer.
Earlier this week, it was revealed Lennon's old school book is to be sold at auction - and is expected to fetch thousands of pounds.
The exercise book contains drawings by the legendary Beatle as a 12-year-old attending a high school in Liverpool.
Teacher Lancelot Burrows was so taken with the pencil and watercolor pictures he kept them to show future pupils at Quarry Bank High. Some of the pictures the future star drew in 1952 illustrate verses from classic poems.
The cover is marked 'My Anthology' and each drawing is marked out of ten in red - the lowest being eight.
It will be sold at a manuscripts auction at Sotheby's next month.