This is an American movie I watched in the 90's. I think it was made early 90's timeframe. This bad guy knocks on these lady's doors, and then viciously attacks and kills them. I remember he came very prepared with ropes and a garbage bag to one of his attacks. The detective chasing him wonders if the killer is insane because of how prepared he is. At some point they ID the killer, and the detective goes to interview his mother. She tells the detective about how her husband was real abusive and would beat her up in front of the son. The father was real violent, but never laid a finger on the son. I think the dad may gave been a neo-nazi, and there is a discussion about whether the nazis were insane.