A pistol attached to a drone... this is probably an NFA violation, yeah?
I believe that's covered with the FFA rules of what is released from a aircraft.
And if the FAA (The FFA is "Future Farmers of America, not sure what they'd have to do with this. heh) wanted to press the issue and find out the real identities of who did this - those folks would be in a world of hurt for weaponizing a drone. Bad juju. Very bad juju.
I always thought we should have a moral discussion about allowing machines to decide when to kill people. Unfortunately, I think we'll walk across that line without any discussion at all. It will be possible, so it will be done and only after the bodies start piling up will anyone wonder how we got there.
Reminds me of Fred Saberhagen's Berserker series...
That discussion has been going on for a few decades.
This is why all my drones have laser weapons. ATF has no jurisdiction.