We have no clue what his relationship with his parents were or his human attachments. He may have mental health issues, and being home-schooled may have made it hard for him to relate to others in his age group who may have had more social experience, sounds like he was in an over-protected environment which may have boomeranged. It is unfair to speculate further, and I am not anti-homeschooling IF the children are provided with social outlets. I only personally know of one home-schooled person who married a home-schooled person.
Right now, I feel very sorry for the family of the shooter, but more may come out about that and I could change my mind. I'm sure glad I didn't go with my first gut reaction.
Understand.