Mark David Chapman (born May 10, 1955) is an American murderer who shot and killed John Lennon at the entrance to the Dakota apartment building in New York City on December 8, 1980. Chapman fired five times at Lennon, hitting him four times in the back, and read The Catcher in the Rye until he was arrested by police. He has repeatedly said that the novel was his statement. Chapman's legal team intended to mount an insanity defense that would be based on expert testimony that he was in a delusional psychotic state at the time of the killing.

Chapman's first court-appointed lawyer, Herbert Adlerberg, withdrew from the case amid threats of lynching. Police feared that Lennon fans might storm the hospital, so they transferred Chapman to Rikers Island for his personal safety. At the initial hearing in January 1981, Chapman's new lawyer, Jonathan Marks, instructed him to enter a plea of not guilty by reason of insanity. In February, Chapman sent a handwritten statement to The New York Times urging everyone to read The Catcher in the Rye, calling it an "extraordinary book that holds many answers." The defense team sought to establish witnesses as to Chapman's mental state at the time of the killing. It was reported they were confident he would be found not guilty by reason of insanity, in which case he would have been committed to a state mental hospital and received treatment. However, in June, Chapman told Marks that he wanted to drop the insanity defense and plead guilty. Marks objected with "serious questions" over Chapman's sanity, and legally challenged his competence to make this decision. In the pursuant hearing on June 22, Chapman said that God had told him to plead guilty and that he would not change his plea or ever appeal, regardless of his sentence. Marks told the court that he opposed Chapman's change of plea but that Chapman would not listen to him. Judge Dennis Edwards refused a further assessment, saying that Chapman had made the decision of his own free will, and declared him competent to plead guilty.

Why did he want to change to a guilty plea?
Chapman said that God had told him to plead guilty