Have you ever read the book, Nudge, by Cass Sunstein and Richard Thaler? Their concept they ironically dubbed, "libertarian paternalism", was highly touted by Barack Obama. Anyway, in that book, they suggest that you only to give nudges and allow people to operate according to the incentives you've laid before them. And it's up to governments to lay out the incentives that work to government's favor.
Anyway, back to this case, just to show a conspiratorial way this would be done.
They have an impressionable kid on SSRI's that visits a gun range.
<Side anecdote, I went to a gun range outside of DC in my teens and I was approached by strangers there that wanted to chat about my political beliefs (I had LP license plates on my truck) - not saying they were agents, but they looked like agents. I even made friends with a guy and we'd meet up there to shoot together until he got too pushy and got angry at me for missing some times that he wanted to shoot. Then, he ghosted me entirely and I never saw him again. Could have just been an $#@!.>
Anyway, they have records of this kid's medical diagnoses, they have records of his range visits and they have records of his online activity. They don't need to ORDER him to do anything, nor do they need to give him the right weapons. The asset will figure that stuff out on his own. They only need to give the proper nudges. "Did you know Trump's having a rally in Butler?" Kid looks up the rally. "I heard the security is so lax at that place - no one's even gonna be watching that AGR building". Agent tracks his phone and sees that the kid is doing recon, so he reports back. They coordinate an opening at the AGR building and let the kid do his thing.
Again, not saying this is how it happened, but it very easily could have.