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 In those brief two shots, you can see that Vera Miles has been replaced by a stiff, rather pale looking dummy.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)
Answer: Norman was found "not guilty" by reason of insanity. Therefore, once he is deemed to be no longer a danger to himself, or to others, and is released from the mental institution, there is no crime he can be sent to jail for (i.e. he has no criminal record for the murders). I haven't done enough research to tell you if a serial killer in recent times has ever been found not guilty by reason of insanity and subsequently been released, but there are numerous accounts of people being released from mental institutions after committing murder that are then considered free.
Bishop73