I don't want to get picky over this but really ...
when a murderer kills somebody, because he is insane, it is still his own fault.
No. That is the whole point! If he was insane he would be judged, "Guilty - but Insane" and he would NOT have been responsible for the murder. Even though he did commit the act.
The man in question (this thread) lost his job and - POSSIBLY - his mind. If you cannot feel sorry for him (as well as his family) then I feel sorry for you.