WASHINGTON — Stephen Paddock, the Las Vegas shooter, had an arsenal of 17 weapons in his hotel room, mostly military-style rifles, according to a law enforcement source.

At least one of them had been modified with a legal “bump stock” style device that allows the shooter to rapidly fire off rounds without actually converting it to a fully automatic weapon, the source said.

The devices modify the gun’s stock so that the recoil helps accelerate how quickly the shooter can pull the trigger. The devices are legal in the U.S.

Other weapons may have been converted to fully automatic fire, and were still being examined, the source said.

Paddock had four Daniel Defense DDM4 rifles, three FN-15s and other rifles made by Sig Sauer.

Paddock apparently bought the guns legally, passing the required background checks.

At least six of the guns were purchased at one store, a Cabela’s in Verdi, Nev. A manager at the store declined to comment.

Several other weapons were purchased at Discount Firearms and Ammo, a few blocks from the strip in Las Vegas, the source said. “It’s an open investigation,” said a store employee, before hanging up.

Paddock, who lived in Mesquite, Nev., also bought some weapons at a store there, Guns and Guitars, according to a statement given by the store owner to USA Today.

“He had good-quality, high-powered rifles,” the source said.

Authorities said today that Paddock had used as many as 10 suitcases to transport the arsenal to his room at the Mandalay Bay and had smashed open the room’s windows with a hammerlike device.

Investigators also found more weapons at his home and are now working to track down all his gun transactions, including some at Nevada gun shows. Records show that Paddock had owned at least 30 guns at one time or another.