Continuity mistake: After Norman argues with Mr Toomey, before he goes up to the house, you can plainly see the light on in the living room where Mary is sitting. When Norman goes in the house, Mary is sitting in the dark and Norman then turns on the light.
Continuity mistake: Norman picks up the note from his "mother" on the order wheel at the diner. He reads it then drops it on the floor. You can see it on the floor yet it's gone when everyone goes back in the kitchen. So where did it go? All the employees were out of the kitchen.
Plot hole: When Norman's doctor follows Lila to Norman's house, by the time he goes into the cellar, the killer has killed Lila, hid the body in the pile of coal, and cleaned up. Highly unlikely in a 4 minute time frame.
Continuity mistake: After Mary takes a shower, she steps out and of course she is completely wet. 3 seconds later her body is completely dry.
Continuity mistake: Norman hits Mrs Spool over the head with a shovel. Immediately after the blow, the camera cuts to an overhead view, and the saucer on the table is suddenly shattered, as is the kitchen chair in which she is sitting, even though they received no direct impact.
Character mistake: There's a note from "mother" on the wheel at the diner. Right beside it is an order with the wrong total. 2 hamburgers for $1.95 each. 2 fries for 90 cents and 2 drinks for 90 cents for a total of $5.70. The waitress put $3.70 for the total.
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