I think this might be the scariest of them all as he seemed like a pretty normal kid. at least in the other situations where these things happened, you went back in their history and there were some trigger points and unique situations that you could point to. Seems like this kid grew up in a reasonably normal household and had a pretty normal upbringing and didn't show any signs of craziness. And then he goes on a random killing spree, not like he even targeted a specific type/class of people, just apparently woke up one day and decided that he wanted to kill random people.
What I am reading is that he was a loner from a deeply fundamentalist religious tightly knit family who was homeschooled.
For a lot of people, including me, that means he was not a "pretty normal kid." It means he was socially and religiously quite different from other kids you might choose at random in the community where he lived. Certainly his whiteness is normalizing, in that he looks like most of the other folks in his community.
Of course were he of any other faith, especially Islam, this act would make him a crazed fundamentalist, a "radical extremist." Christianity earns him a pass for the moment.