Forty-seven guns were found in the suspected Las Vegas shooter's hotel suite and two homes, police said Tuesday night at a press conference.
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Multiple loaded high-capacity magazines were found in the hotel suite, at the Mandalay Bay Resort and Casino, law enforcement sources said on Monday.
Among the guns and ammunition that police found in the rooms being used by gunman Stephen Paddock were some high-powered rifles considered capable of penetrating police armor. There were also some handguns in the suite.
Police said the guns were purchased in Nevada, California, Utah and Texas.
The additional ammunition indicates that the shooting, which left 58 people dead and injured over 500, could have been worse, had police not intervened when they did. Police believe that Paddock killed himself shortly before police reached him.
A modified bump stock rifle was also found, which allows a gun to simulate rapid automatic gunfire. Law enforcement officials are still in the process of examining firearms to determine if they were capable of firing automatically.
One official said Paddock had a camera mounted in the room, apparently to record himself.
At a separate location authorities found tannerite, an explosive used in target practice, sources said.
Earlier, Clark County Sheriff Joseph Lombardo said there were at least 10 rifles in the suite but noted that the investigation was still underway.
The Bureau of Alcohol, Tobacco, Firearms and Explosives released a statement announcing that it is "currently conducting an urgent trace on firearms recovered from the scene in Las Vegas."
The shooting is the deadliest in modern U.S. history.
A gun shop owner in Mesquite confirmed for ABC News that he sold guns to Paddock, but he did not specify how many or whether they were the ones used in the shooting.
"We mourn for this tragedy, and our thoughts and prayers are with the families of the lost and injured," said Christopher M. Sullivan, the general manager of Guns & Guitars Inc.
"Mr. Paddock was a customer and purchased firearms from our store; however, all necessary background checks and procedures were followed, as required by local, state and federal law. He never gave any indication or reason to believe he was unstable or unfit at any time. We are currently cooperating with the ongoing investigation by local and federal law enforcement in any way we can," Sullivan said.
Guns & Guitars sells semiautomatic weapons but not fully automatic weapons.
Another gun store owner confirmed for ABC News that he sold a shotgun to Paddock in February.
Chris Michel, the owner of Dixie Gunworx, told ABC News that Paddock visited his store three times. "He was an average everyday Joe Blow guy," said Michel. "I remember his face, his name, him coming in."
The purchase was "legal in every way," Michel said, adding that he is in touch with law enforcement.
John Cohen, a former Department of Homeland Security undersecretary who previously worked as a police officer, said that recordings of the shooting suggest that the shooter used an automatic weapon.
"Listening to the video. It sounds like the weapons were fully automatic," said Cohen, who is now an ABC News consultant.
He said that when a gun is automatic, that means "you pull the trigger once and rounds are fired in rapid succession."
"[The bullets] were coming out very quick, and you heard a large number of shots very quickly. That would be very difficult to do with anything other than an automatic weapon," Cohen said.
"It's not legal to purchase a fully automatic weapon, but it's not that difficult to convert legal semiautomatic weapons so that they are fully automatic," he said.
ABC News' Pierre Thomas, Jack Date, Mike Levine and Lauren Pearle contributed to this report.