Since it wasn’t for me, (I know tricks which work on paywalls about half the time), I’ll cut to the chase:
The editorial bent of this story is ZOMG 2ND AMENDMENT PRIVACY LOL~!!!!!1
All I need to know is where it was happening: Southern California, and especially suburban San Diego.
Which means the purpose of doing it is to try to catch drug cartels before they make their way across the border with what they procured at these shows. Or, if not that, to assemble a nice paper trail for U.S. Attorneys’ future use.
I wouldn’t be so upset with this, if I already didn’t know that at about this same time, the Obama Administration was practically directly arming Mexican drug gangs and cartels, in a devious attempt to sandbag both American domestic immigration politics and 2A politics.