The death toll in the massacre in Las Vegas has risen to 59, Nevada Sheriff Joseph Lombardo said on Monday evening.

527 people were wounded in the shooting, the deadliest mass shooting in U.S. history.

Lombardo also told a news briefing that 18 firearms were discovered in the Mesquite home of the shooter, Stephen Paddock.

Earlier, officials told The New York Times that at least 20 rifles were found Paddock’s hotel room after the shooting, along with hundreds of rounds of ammunition.

Among the guns found were AR-15-style assault rifles, one official said.

64-year-old Paddock was found dead in his room at the hotel following the shooting.

The Islamic State (ISIS) terrorist organization claimed that Paddock was a convert to Islam and one of their fighters. However, the FBI later debunked the terror group's claims.

Law enforcement officials are still working to determine what may have motivated Paddock, who was described as “aggressively unfriendly”, to commit the mass shooting, Fox News reported.

Paddock of was a gambling multimillionaire who made much of his money investing in real estate, according to his brother, Eric, who added that he had no reason to believe the gunman had run into financial trouble.

“No affiliation, no religion, no politics. He never cared about any of that stuff,” Eric Paddock was quoted as having told reporters. “He was a guy who had money. He went on cruises and gambled.”

He described his brother as a multimillionaire and said they had business dealings and owned property together. He said he was not aware that his brother had gambling debts.

“He had substantial wealth. He'd tell me when he'd win. He'd grouse when he'd lost. He never said he'd lost four million dollars or something. I think he would have told me,” said the brother, according to Fox News.