When the gunshots started, videos showed, those in front of the stage dropped to their stomachs — often an adequate first measure when under fire. But on Sunday night, the decision potentially put them at greater risk.

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.

Weapons capable of burst fire have long been federally regulated in the United States and are more difficult to obtain than weapons that fire semiautomatically, for which regulations vary by state.

It was not clear on Monday evening whether Mr. Paddock possessed such weapons, or used semiautomatic weapons that had been altered. In some videos of the shooting, the rate of fire sounds inconsistent, at times sputtering.

This suggests the possibility that a weapon could have been modified to fire more quickly, a change to semiautomatic firearms known as bump or slide fire. Such modifications harness the recoil to allow for rapid fire.

Sheriff Joseph Lombardo of Clark County, Nev., said that at least 16 rifles, ranging from .308 to .223 caliber, and a handgun were retrieved from Mr. Paddock’s hotel room. A federal law enforcement official said that AR-15-style rifles were among them. The authorities did not detail all of the guns, or which weapons Mr. Paddock fired.

Mr. Paddock had purchased some guns in Arizona, according to a gun seller there who spoke with the authorities.