I think you have to be psychologically damaged to commit a crime like this anyway. But even if not, after its done, I think a killer does mentally distance themselves from what happened rather than actually deal with what they have done. I don't know, I am sure people study this sort of thing. I just can't imagine being in that situation. Facing life in prison, knowing you will never again be free, never get to hold his daughter, or eat a good meal again, never get to walk in the sun. Add on the horror of dealing with the fact that you ended a beautiful life. Unimaginable.