The creation of the murderer. Watch
Are murderers simply grown adults who in too much effect have had an unhealthy childhood relating to how their parents, idols, or peers had treated them? Is it in the blood, a gene that drives people to the madness of killing others? It's obviously a disorder, but is it a disorder you could classify someone with before they commited the crime?
i don't think you can classify someone before they have done something, sometimes normal persons commits the most horrible crimes and nobody knew it was coming
What about in the case of a cerial killer, where it is not just jealousy, or defense that had caused the death?
i don't know, however i don't think that all killers do it for the same reason