Re. the Las Vegas shooting. It's pretty unrealistic to attempt to defend an event, in an urban environment, against a lone sniper unless you have the Secret Service and the FBI to call upon. I can imagine that a couple yrs down the road the military will have small drones capable of deadly force. Not big-ass things with Helfire missiles, I mean little things that would hover a couple hundred feet up unnoticed. The military versions would probably fire some kind of small anti-personnel rocket. HE or AP (armor piercing) warhead. A little guided rocket could be made much lighter than a rifle sort of weapon. A couple years later, they'd show up for police duty, with the AP warhead replaced with something less penetrating.

Then the event could pay for a police anti-sniper drone just like they pay for additional police security for their event. I'm not talking autonomous, mind you. We can't have Skynet deciding whether to bring deadly force to bear. Then, in the unlikely event that a sniper has picked that event to attempt a massacre, the anti-sniper drone could, aided by acoustics, zip over within range and take out the bad guy in seconds.

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"If only he had used his genius for niceness, instead of Evil." M. Smart