Revealing mistake: When Toomey is at the motel packing his clothes after Norman fired him, he is startled by "someone" and he turns around and gets slashed with a knife in the face. Before Toomey gets slashed though, you can see a prosthetic scar on his face and a wire in the top right hand corner to trigger the prosthetic scar to open up and look like a knife wound. (00:38:40)
Revealing mistake: When Lila gets killed, the knife goes through her mouth and emerges at the back of her neck. In those brief two shots, you can see that Vera Miles has been replaced by a stiff, rather pale looking dummy. (01:25:35)
Revealing mistake: At the end when Norman is being stabbed at by Mary dressed up as Mother, Mary stabs Norman in the hand. You can plainly tell that this hand is a doll, as it is not a natural colour, it is stiff and is stationary, unlike Norman who is moving his hands. (01:35:10)
Revealing mistake: When Norman hits Mrs. Spool over the head with a shovel, she falls to the ground. In the brief shot of her falling, you can see Mrs. Spool is a dummy. Also later when he carries her up the stairs, she is a dummy. (01:43:25 - 01:44:05)
Chosen answer: The murderer is Emma Spool, Norman's biological mother. She was killing people because she didn't want anybody harming Norman.
Emma was not Norman's biological mother. She was the sister of Norma (and Norman's aunt) and jealous that Mr. Bates chose Norma over her and thought Norman should have been the son she and Mr. Bates were suppose to have. Later, while still mentally ill, she believed Norman was her son and told Norman this.
Bishop73
Emma Spool was, in fact, Norman's biological mother. It was revealed at the end of the movie that she is his real mother and Norma Bates is her sister who adopted Norman and raised him While Emma was institutionalized.
ctown28 ★
Again, that was just Emma being delusional and/or lying. Tracy Venable tells Norman the truth in Psycho III. Emma was never his mother.
Bishop73
I never knew Emma Spool was Norman's biological mother. In fact, I never heard of Emma Spool. Thanks.