Yeah, but you gotta love that these people are so stupid they think they can just walk into federal buildings with a rifle as if they were the entire mob of January 6th insurrectionists.
Based on pics it looks like a rifle that's not legal in DC due to it having too many features, and probably the named/clone ban.
Being from Atlanta I presume the fellow did not take the 16 hour class to put in for a DC carry permit, which doesn't let you open carry or carry on the mall.
That's a felony for the firearm, carrying it, one for each bullet, and each magazine over 10 rounds.