Question...how was JB involved in the killing?

Dr. Murchison didn't need to know John would assume Dr. Edwards identity. In fact, John's assumption of Dr. Edward's identity worked against Dr. Murchison.

John's burn is from a plane crash. Because of the crash, he meets Dr. Edwards. As part of John's therapy, Dr. Edwards suggests John join him in a skiing trip in Gabriel Valley. But first, Dr. Edwards and John have lunch at the 21 Club.

At the 21 Club, Dr. Murchison accused the real Dr. Edwards of stealing his job (in John's presence). Murchison then follows Edwards to Gabriel Valley and waits for Edwards on the slope near a cliff. Murchison shoots Edwards, who continues his downward momentum and skis off the cliff. By shooting Edwards, Murchison gets rid of his replacement -- someone Murchison believed stole his job.

John is several feet behind Edwards and witnesses the event. John may be neurotic but he is not insane. Because of his guilt complex from his tragic past, Edwards' death shocks John into losing his memory. Because his psyche cannot accept Edwards is dead and because he feels irrationally responsible, John assumes Edwards' identity (Edwards cannot be dead because I [John] am Edwards). John is not posing. He believes he is Edwards.

Imagine Dr. Murchison's surprise when John appears at Green Manor as Edwards. He believes he has murdered his replacement, and a replacement still shows up. If he "outs" John, Murchison admits having met Edwards, and risks John remembering the argument at the 21 Club. If you murdered someone, would you want people remembering you had an argument with the victim before his death?

Constance's observation of John's burn starts the ball rolling in the recovery of his memory.

The Salvador Dali arrangement added to the plot. It gave enough of what happened away for Constance to solve a portion of what happened, but did not explain how Edwards was shot or who shot Edwards. Besides, dreams are not always linear or even coherent.

It's all clearly explained in the movie.

John and Dr. Edwards were eating lunch together at the 21 Club. Dr. Murchison, who had been going through recent psychiatric troubles, knew Dr. Edwards was going to replace him at the hospital and picked a fight with him at the club. Afterward Dr. Murchison followed John and Dr. Edwards to the ski resort, where Murchison shot Edwards. Edwards' dead body slid off the cliff.

John, who had accidentally killed his brother by sliding down a bannister and knocking him into an spiked gate, flashed back to this previous trauma and thought he was responsible for the murder. Murchison was acting psychotically and irrationally. He didn't need to know about John's complex; it was just a lucky break for him.

"If John went to Dr.Edwards for treatment and not Dr.Murchison, how did Murchison know about John's history? Further after the death of Dr.Edwards, if John is sane enough to pose as Dr.Edwards and go to Green Manor, how come he cannot remember the face of the killer with the gun or the face of person who confronted Dr.Edwards in the 21 Club? Add this to the surrealistic gibberish of Salvador Dali and this makes Hitchcock the Classic Spin Doctor - something similar to Richard Burton in 'Where Eagles Dare'. Everybody acknowledge it to be a great movie and nobody has fully understood it. "



Seemingly the only one who hasn't fully understood it is you.

Honestly, did you even watch this? The killing and the fall over the cliff triggers the memory of killing of his brother, the amnesia, and the subsequent taking over of Edwards personality. So obviously with amnesia he cannot remember the face of the real killer. Hence the blank face of the proprietor in the dream. Considering it by 1945 standards the Dali dream sequence is one the most hauntingly brilliant in film and still highly regarded. I wasnt aware Hitchcock was attempting to be a psychologist just by making a film, if one wants to take is as any more than that, then good luck to 'em.