>> mark david chapman has plead guilty by reason of the insanity to the killing of john lennon. >> to the sr. prize of everyone in the courtroom, chapman pled guilty and was sentenced to 20 years to life. he never stood trial. >> my reaction was disappointmentment. i was disappointed because i thought that there were lessons to be learned for this case. >> lessons that ken holgrief still cites to this day. >> the most common impression that one gets when you hear people talk about the murder of john lennon is they refer to a crazed beatle fan. he wasn't crazed. >> but you're saying a trial would have proved that this was not about a crazed john lennon fan. >> correct. >> this guy was a killer and he was going to kill anybody just to become famous. >> yes, he is guilty of a heinous murder. >> do you think that he would kill again? >> i think it is possible. >> you never know what is going to happen.