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The shooter who gunned down 59 people and injured over 500 at a Las Vegas country concert Sunday night seems to have bought his plethora of guns legally.

Police found 23 guns in Stephen Paddock's hotel room where he aimed an automatic rifle at the crowd below as well as 19 more guns at his home. Authorities also discovered 20 suitcases in the hotel room.

Paddock filled out the form from the Bureau of Alcohol, Tobacco, Firearms and Explosives for all of his weapon purchases, William La Jeunesse reported from Los Angeles. The form starts the FBI background check and includes a home address, any criminal record, and history of mental illness.

Paddock's purchases included six from a Reno dealer, some from the Great Western Gun Show in Phoenix, and a shotgun from a Utah store.

"No red flags, went through the entire background check, all different safety checks were checked off, FBI passed him off through the system," said Chris Michel, owner of the Utah firearms store.

Police believe the shooter converted his semi-automatic weapon to an automatic weapon, using a process known as bump-firing.

La Jeunesse said one expert told him he heard a continuous burst of 75 rounds in the footage of the attack.

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