Late musician John Lennon's former personal assistant is convinced the singer's lack of security led to him being murdered.

Actor and mime artist Dan Richter, 83, who lived and worked with John and The Beatles' icon's wife Yoko Ono as their PA from 1969 to 1973, said the music legend should never have been using the front door of the New York City apartment building where he was assassinated 42 years ago this month, reports aceshowbiz.com.

Dan, who starred as the lead man-ape in the opening scene of Stanley Kubrick's 1968 epic '2001: A Space Odyssey', told the Daily Telegraph on Wednesday "that door was a danger point".

"You can identify and avoid that. And there was a side door he could have used."

He also recalled fearing John was about to be murdered on a visit to meet Bob Dylan at the Plaza Hotel in New York.

Dan got out of the car first to check the area were safe but was left terrified by a man speedily approaching them while reaching into his pocket.

"I thought I was going to die. Turned out he was hotel security coming to see if we needed help! Then I realised Bob was standing there all the time, totally unnoticed, in camouflage fatigues, laughing."

Dan also told how he never thought Yoko would be a target for assassination despite the fact "people really did hate her" after she was blamed by fans for breaking up The Beatles.

Paul McCartney said earlier this month he couldn't bear to talk about Lennon's death after the singer was assassinated.

The 80-year-old rock veteran's former Beatles bandmate was gunned down outside his apartment in New York City on December 8, 1980, leaving behind his wife Yoko and sons Sean and Julian.

McCartney opened up about his devastation over Lennon's death in an interview for 'The Beatles Channel' on SirusXM, saying: "When John died it was so difficult. It had hit me so much so, that I couldn't really talk about it. I remember getting home from the studio on the day that we'd heard the news he died.

"Turning the TV on and seeing people say, 'well, John Lennon was this', and 'What he was, was this', and 'I remember meeting him' and it was like, 'I don't know, I can't be one of those people'. I can't just go on TV and say what John meant to me. It was just too deep. It's just too much. I couldn't put it into words."

Lennon was shot in the back five times outside his Dakota apartment building by Beatles fanatic Mark David Chapman, now 67, hours after the singer spoke to him and signed one of his records.

The killer, infamously carrying a copy of J.D. Salinger's "The Catcher in the Rye" novel with his pistol, stayed at the scene of the murder until he was arrested by police, and is still languishing in prison after 12 of his parole bids were denied.