A Slasher Movie Question...
 

The movie is a slasher from '80's.

There is this psycho killer who had a terrible childhood. In one scene we see the killer as a kid. His mother is dressed for making love, with stockings, black underwear and a black sexy robe. She and her lover are in the kitchen making love. The kid wakes up and comes to kitchen, he watches the scene and then his mother sees him but she doesn't care. Then the boy takes out a knife from the shelf and kills the guy and the mother. (I'm not sure with the killing of the mother)

In antoher scene I remeber a caravan, inside there is an old man with a cowboy hat and a prostitute with him. Our killer comes and kills them all.

.....

Anybody remember this movie?

Sounds like The Boogey Man (1980).

Are there any screenshots? I was thinking about the Boogey Man but cannot be sure about the kitchen scene. Could it be Patrick?

I did find this:
http://www.bizarreingredients.co.uk/...gey/bogey.html

could be Nightmare (1982). I don't remember a caravan in Boogey Man