Predator drones? Ten million of them ready to strike at the report from one rifle on the ground? Pretty pricey and still after the fact.
Spy satellites? Watching 320 million people looking for that guy down there ratcheting the bolt on his Remington 700? They can't find the illegal alien who comes to work at the same place every day.
Online surveillance and communications systems? Finding what? The 1% of guys who are dumb enough to post "I'm going out to take my shot today." Sure. I think I'm being very generous to that position to suggest 1% would be that stupid.