The possibility that Mr. Paddock used tripods, which two law enforcement officials said were in the room, indicates that he understood how to overcome some of the difficulties of his plan. Special mounts designed to fit the underside of a rifle and sit atop camera tripods allow the gunman to fire more accurately while standing. Military snipers use tripods in urban spaces, often setting themselves back from a window so neither they nor their weapons can be seen from the streets below…

Mr. Paddock’s position overhead gave him a vantage point over objects and obstacles that would typically protect people from bullets flying from a gunman at ground level. It also meant that inaccurate shots — the sort common to rapid or hurried fire, which typically sail high or strike the ground short — could still plunge into areas where people were huddled.

Audio recordings of the shooting suggest that at least one of Mr. Paddock’s weapons fired automatically, discharging multiple bullets with a single depression of a trigger, in what are commonly called bursts.