Every thing around him could take on a special significance; every word of every song was speaking to him; images on television were aimed at him; the text of a book had been written especially for him; a painting could be sending him a secret, coded message.

And to the paranoid schizophrenic, these signals must be responded to. Such individuals see themselves as a champion on a quest. They can see themselves as a Saviour, someone who has been given a special signal and a special mission.

Mark Chapman saw signs and signals and synchronicities at every turn - he heard the signs in the lyrics he listened to, saw signals in the album covers, and on tv, in the paintings he collected, and in the books he read.

• On Todd Rundgren's "Adventures In Utopia" album, he listened to high-pitched coded signals and was fascinated by the album's inner sleeve, which he saw as a television "testcard", designed to help fine tune reception of his special signals.

• Mark Chapman began collecting particular works of art during 1979 and 1980, because in them, he recognised the signs and signals of narcissism and split personality that he had been searching for, and they gave him confirmation that he had been chosen to perform this special mission.

• The idea of a split personality was reflected in Todd Rundgren's lyrics and album covers, like "A Wizard/A True Star", and later, by Norman Rockwell's painting "Triple Self Portrait"  which introduced the idea of a three-way split: Lennon, Chapman and Holden Caulfield.

• Mark Chapman felt he was receiving special broadcast signals telling him to read Salinger's novel "The Catcher In The Rye" . With each page read, he felt that he was becoming Holden Caulfield, the "Catcher", whose role was to protect little children from harm.

• When the signals first pointed to Lennon as the target, Mark Chapman researched what the rock star had been doing in the last few years. With rising anger, he read about Lennon's luxurious and reclusive lifestyle and phoney posturing in Anthony Fawcett's book One Day At A Time . The book gave him all the confirmation he needed - Lennon was a big phoney and deserved to die.

• But as he listened to Lennon's songs on the  "Double Fantasy" album in October 1980, it seemed that Lennon was posing as the new "Catcher" - Mark reacted angrily: he was the real Catcher and Lennon was the impostor.

• Chapman's disturbed mental state meant that he was confused about his own identity, at times he felt he was John Lennon, at times Holden Caulfield, at times Mark Chapman.  

• By early 1980, Chapman had come to regard Lennon and himself as a kind of twinned personality or doppelganger. (The "doppelganger": two personalities sharing the same time and space, and one has to cancel out the other. Some see the doppelganger as an expression of the ideal self in conflict with the actual self - perhaps this was the real conflict in Mark Chapman. There has always been a question mark over whether what he did was murder or a kind of surrogate suicide.)

• And by 1980, there was a further complication - there was now a 3 way split in his personality: he saw himself as Mark Chapman, John Lennon and Holden Caulfield. He signed off from his job in Hawaii as "John Lennon" and made it his mission to eliminate this other side of himself, so he could become Holden Caulfield.

• To Chapman, the connection with "The Catcher In The Rye" was overwhelmingly clear.

  The one time that Chapman really felt good about himself was when he worked in Fort Chaffee camp for Vietnamese refugee children. He was like a Pied Piper to the children: playing his guitar, singing songs for them. They loved him and followed him around the camp. It was almost the only thing in his life he felt a sense of pride about, and he looked back on those times and longed to re-establish himself as some kind of protector of children, some kind of Catcher In The Rye, a book he remembered from High School, and which he now read and re-read.

  Chapman had now come to see himself as a new Catcher In The Rye, protecting the children, keeping them away from the dangerous evils of the world.

  But now, here was Lennon singing as if he was the new protector of children.

  It was all coming together, and all he had to do was follow the signals.