I got the whole story, but not from Norman. I got it from his 'mother'. Norman Bates no longer exists. He only half-existed to begin with. And now, the other half has taken over, probably for all time...
Now, to understand it the way I understood it, hearing it from the 'mother', that is, from the 'mother' half of Norman's mind, you have to go back ten years to the time when Norman murdered his mother and her lover. Now he was already dangerously disturbed, had been ever since his father died. His mother was a clinging, demanding woman, and for years, the two of them lived as if there was no one else in the world. Then, she met a man and it seemed to Norman that she threw him over for this man. Now that pushed him over the line and he k**ed them both.
Matricide is probably the most unbearable crime of all - most unbearable to the son who commits it. So he had to erase the crime, at least in his own mind. He stole her corpse. A weighted coffin was buried. He hid the body in the fruit cellar, even treated it to keep it as well as it would keep. And that still wasn't enough. She was there, but she was a corpse.
So he began to think and speak for her, give her half his life, so to speak. At times, he could be both personalities, carry on conversations. At other times, the 'mother' half took over completely. Now, he was never all Norman, but he was often only 'mother'. And because he was so pathologically jealous of her, he a**umed that she was as jealous of him. Therefore, if he felt a strong attraction to any other woman, the 'mother' side of him would go wild. (To Lila) When he met your sister, he was touched by her, aroused by her. He wanted her. That set off the jealous 'mother', and 'mother' k**ed the girl. Now after the murder, Norman returned as if from a deep sleep, and, like a dutiful son, covered up all traces of the crime he was convinced his 'mother' had committed!...
In Norman's case, he was simply doing every thing possible to keep alive the illusion of his mother being alive. And when reality came too close, when danger or desire threatened that illusion, he'd dress up, even to a cheap wig he bought. He'd walk about the house, sit in her chair, speak in her voice. He tried to be his mother. And, uh, now he is. Now that's what I meant when I said I got the story from the 'mother'. You see, when the mind houses two personalities, there's always a conflict, a battle. In Norman's case, the battle is over, and the dominant personality has won...These were crimes of pa**ion, not profit.