I don't know how a massacre would be any kind of FBI sting, but then again, I don't know much.
Paddock; noun
1.a small, usually enclosed field near a stable or barn for pasturing or exercising animals.
2.the enclosure in which horses are saddled and mounted before a race.
It’s actually pretty simple. Terrorists walk in to buy guns, security guard spooks them, they shoot the guard, shoot the dealer(Paddock), and then opportunistically use the weapons for ten minutes.