Whether you like his music or not, Mark Chapman is a very sick man who should never be let out of prison. Similarly Yoko Ono is very weird for having a bronze cast made of John's torso showing the position of the bullet holes...
The music is ok but not as great as made out and the lyrics tend to be trite and sub sixth form. There is a great deal of pretension in the whole boiling and quite frankly I would have as much care about it all as Wellington did about what happened to Napoleon's ashes.
Years ago I read a book about Lennon's death which was just peddling a conspiracy theory. I'm glad that didn't "take", or I might have gone down a rabbit hole of the damn things.