But, you have ideological and emotional company. We have some Alaskans out there wanting to know why folks in the effete East chose to go around unarmed. They note that "back home" they'd shot this perp to pieces.
This always requires a long story about Virginia not being part of Maryland, and we have guns - big guns - actually really, really, really big guns, and they have to give us a permit to carry a concealed weapon, which is why all adult males walk with a limp - it's from the rifle or shotgun down their britches!
Leastwise some folks think that. In any case, the situation at the Home Depot involved dozens of people running and screaming. This spoiled the shot. Besides, the witnesses knew how valuable they were alive, and it was clear the guy was ready to rock and roll with bursts of 4 from his AK-74~ ~ ~ ~ / ~ ~ ~ ~ /
My guess is the witness described something, possibly mentioning the AK-47, and the cops/feds figured it out. It's possible they already knew from the bullet signature.