ATF officials confirmed on Tuesday that alleged Las Vegas gunman Stephen Paddock augmented 12 firearms with bump-fire stocks to allow for semi-automatic weapons to mimic automatic gunfire. 

Using bump stocks allowed for Paddock to fire ammunition into the crowd at a faster rate.

Because it does not mechanically alter the weapon, ATF spokesperson Jill Snyder said that these devices are not illegal to own. 

While authorities have not announced the type of weapons of Paddock used Sunday night, Paddock had a total of 23 weapons with him in a Mandalay Bay hotel room. All told, authorities uncovered 47 weapons. 

A search warrant allowed for authorities to uncover 19 weapons from Paddock's home in Mesquite, Nevada, and five at his home near Reno. The weapons were purchased in Nevada, California, Utah and Texas.

Paddock had rifles, shotguns and pistols, Snyder said. 

ATF confirmed that Paddock continued to fire on the crowd below for a period of nine to 11 minutes.