Las Vegas law enforcement found the shooter in Sunday night's attack had explosive devices and more than 40 weapons at his home and hotel room.

Investigators found an alarming arsenal of 23 weapons in the suspected shooter's hotel suite, including semiautomatic rifles, scopes and hundreds of rounds of ammunition. Here at KVUE, we wanted to see how easy it is to get those guns.

We found out it is legal to own an automatic weapon if that gun meets certain criteria.

The Firearm Owners' Protection Act of 1986 says civilians are not allowed to own newly manufactured machine guns. However, if they were built before May 1986, they can be lawfully registered, owned and sold.

"It's no different than walking into a gun store and getting a background check there," explained Michael Cargill, owner of Central Texas Gun Works. "It's the same type of background check. The only difference is that particular weapon is actually registered with the ATF and you pay a $200 tax stamp fee."

A Bureau of Alcohol, Tobacco, and Firearms report shows that as of 2006, the most recent information we could find, 391,532 machine guns were registered.

In the same year, the ATF seized 1,280 unregistered machine guns.

Cargill says the ATF and the FBI likely already know where the gun used in the attack came from, where it was made and sold and who bought it.