I saw a program on the Green River murders. Very gross and interesting. I believe most of his victims were prostitutes (the sex kind not the political or business kind).
This guy is a severly sick individual (goes without saying).
Another person who was mentally, physically and if I remember correctly sexually abused as a child. Another child who didn't receive love or nurturing in his developing years. Unable to form healthy relationships due to the abuse and neglect.
It's no excuse for any crime though.