Most likely a false flag, FBI or CIA set up a “nut”, provided him with the weapon and ammunition and encourage him to do this. This guy was most likely under long term psychological care and on medication. This is the Alphabet Agencies MO when the seek to “trick” these people into performing such deeds. After the Military take over of DC, they need to catch someone to avoid looking more foolish then they already do.
Can't send a Virginia Man to do Florida Man's job.