If I murdered my wife and child by cutting their hearts out and fully understood what I had done...I'd not only want to be dead, I'd think I deserved it. If I felt guilty of commiting the murders, and felt the full crushing burden of the guilt of murdering my wife and baby girl, two people I was supposed to be protecting, IMHO, the only possible reaction of a sane person...I'd think death was proper punishment.
If I didn't feel guilty but fully understood what I did in the throes of insanity, and understood the full horror of those actions, which in itself sounds like a pretty insane and completely disassociated state of mind...I'd consider death a merciful release or else I'd be as insane as I was when I disassociated from the actions in the first place.