While investigators reveal more information regarding the firearms discovered in a Mandalay Bay hotel room following Sunday's devastating shooting in Las Vegas, questions regarding the modifications to the weaponry surfaced.
Since the shooting, it's been revealed that a device called a "bump-fire stock" was discovered on firearms found in suspected shooter Stephen Paddock's hotel room.
A bump-fire stock "uses the recoil of a semi-automatic firearm to fire multiple shots in rapid succession," according to the company Slide Fire, which manufactures the specialized stocks.
A semi-automatic weapon can only fire one shot per trigger pull. Bump-fire stocks allow semi-automatic guns to mimic automatic firearms by bumping the trigger - using the recoil of the gun bouncing backward with each shot - into the user's finger.
As the trigger bumps into the user's finger, this creates a higher rate of fire. The user doesn't need to manually pull down on the firearm's trigger. The user simply needs to push forward on the front grip to push the trigger into their finger as recoil takes over.
Bump-fire stocks are legal. Companies such as Slide Fire have argued that the stocks do not contain any mechanical parts and thus do not alter a firearm's function to fire automatically. Instead, the device allows for "an alternate shooting technique," creating, "reliable rapid fire," according to Slide Fire.
Jill Snyder, ATF San Francisco field division special agent, said Tuesday that the bump-fire stocks located in Paddock's room were legal:
"The ATF Firearms and Ammunition Technology Division provides determinations on devices such as bump fire stocks and their legality. The classification of these devices depends on whether they mechanically alter the function of the firearm to fire fully automatic. Bump fire stocks, while simulating automatic fire, do not actually alter the firearm to fire automatically, making them legal under current federal law."
Investigators Tuesday said 12 bump-fire stocks were found on firearms discovered at the scene. Police reported recovering 23 firearms in Paddock's hotel room, though officials are still working to determine which weapons were used in the shooting.