I haven't really seen this confirmed, but lots of people saying one of the women in the hospital is his wife. Several people have said he got caught cheating on her. Take that as rumor but it would explain his annihilate behavior.
It's being reported that this started as a domestic dispute so I wouldn't be surprised that one of the women who were shot was in a relationship with the killer.
I can see being mad at a partner but why in God's name kill all of your kids over it?