umm... you just contradicted yourself twice in the same paragraph. First of all, you have this almost completely ass backwards. There are plenty of non-crazy people who have killed women, wives, gang members, etc. You don't need to be crazy to kill your wife. HOWEVER, you are right. Only the sickest person could kill a child. However unlike you I don't mean "sickest" to be some unqualified derogatory term. I mean sick, with problems, not all there, not playing with a full deck.
I agree that killing his kid elevates this to an entirely different act of violence, but again for an entirely different reason. If he had just killed his wife and then were arrested I don't think a single person here would be saying "I wonder what happened". We would ALL be saying "Well, here's another Austin. Who knew?" or some such. But killing his kid shows that obviously this wasn't a typical domestic violence. Obviously this wasn't some pattern of abuse manifesting itself. The killing of his child by default implies there was a lot more to it here than just some abusive asshole showing his woman who's in charge. If you can't see or understand that, then you really have very little understanding of what domestic abuse is about and what obvious clinical signs of mental illness are. They are all readily apparent here.
Assholes beat their wives and sometimes kill them. Crazy people kill their families, kids and all, and then commit suicide afterwards. Not too hard to understand really.