He killed more adults than children; from what has been released so far, his motives do not seem to have been rooted in excitement.
And, as winnybella has been saying, it seems that a lot was known about him. And I hope there will be a full investigation into why the deaths of the soldiers (from which the significant lead from the email address arose) was not pursued with far greater vigour. Had it been, could the school shootings have been avoided?