I am back. But I see there is, after all, little more to add:
The official said that Mr. Dear "said a lot of things" during his interview, making it difficult for the authorities to pinpoint a specific motivation.
Allow me to exercise my speculative muscles a bit more. Mr. Dear's motivation was that of a GOTV precinct captain for the GOP; he learned public policy at the cloven feet of Carly Fiorina; and he worships the rhetorical coherence of Ben Carson and Donald Trump.
And his, my friends, is a classic portrait of your average Republican primary voter and contemporary-conservatism enthusiast. As GOP presidential hysteria pursues the vote of every last mad American, we can expect more of these crackpots with perfectly legal and sophisticated weaponry to emerge from other meccas of Christian insanity or hotbeds of Beckism, whereupon they will exercise their First and, above all, Second Amendment rights.
USA. We're #1.
I shall be back full-time in the morn, cheerful and optimistic as ever.