This sort of thing simply transcends my capacity to comprehend.
This is a breaking story, and nobody knows much. His wife and oldest daughter were not at the house at the time. Folks will soon be speculating as to the cause. Maybe he had PTSD. Maybe he was in a failing marriage. Maybe it is a culture that devalues women and looks the other way at male violence towards female family members. Whatever. None of that means anything to me.
As the father of a daughter, I simply cannot grasp the cognition of a father who could ever even entertain in his head the idea of killing his own daughter.
(I edited the original to emphasize the speculativeness of my examples of speculated causes ... at this point, the news on the story has no information of any kind that gives us any understanding at all of the man's possible motivations.)