The gunman in the deadliest mass shooting in U.S. history is thought to have killed himself in a hotel on the Las Vegas Strip before police could get to him, law enforcement said Monday.

As of 6:00 p.m. ET, 59 people were dead and 527 were wounded in the shooting at a country music festival across the Strip from the Mandalay Bay Casino, where 64-year-old Stephen Craig Paddock is thought to have sprayed bullets from a hotel room.

Officials found more than 10 rifles in a hotel room, according to Las Vegas Metropolitan Police Department Sheriff Joseph Lombardo during one of several news conferences.

Lombardo said police found Paddock dead in the hotel room, which he checked himself into Thursday, Sept. 28.

Paddock's brother, Orlando-area resident Eric Paddock, said that "something incredibly wrong happened to my brother."

Lombardo said that Paddock was firing rounds from the 32nd floor at thousands of people at the outdoor concert after he smashed the windows from his room. Paddock did not show up in any criminal databases, Lombardo said.

During a fourth news conference on Monday, Lombardo said the FBI has joined the investigation. Special FBI agent Aaron Rouse said that there is no connection between Paddock and any international terrorist organization, though the Islamic State tried to claim responsibility for the shooting.

The Las Vegas mayor said what happened in the city is not what its people are about.

"This is a crazed lunatic full of hate. We don't know much about his background, but it is certainly not an extension of what we believe in …," she said.  

Anyone looking for loved ones should call 1-866-535-5654, Lombardo said, who added that it will take a long time for investigators to identify the bodies from the concert venue and notify families.

Before police can investigate Paddock's Mesquite, Nevada home, they have to clear his house of any possible explosives, Lombardo said. He also said Paddock had other property in northern Nevada that they will investigate. 

Country music star Jason Aldean was performing on stage when the shots began ringing out just after 10 p.m. Sunday local time at the Route 91 Harvest Festival. Several officers from the Bakersfield Police Department were attending the festival when the gunman opened fire.

The two slain off-duty officers were attending the concert, Lombardo said. Two on-duty Las Vegas officers were wounded Sunday night. One had surgery; the other sustained minor injuries.

Lombardo said police think this was a "lone wolf" attack, meaning they don't think anyone else was involved.

 

The Pulse nightclub shooting left 49 people dead by gunman Omar Mateen, who was killed by law enforcement.

President Donald Trump tweeted his condolences.

Stephen Paddock's father was a notorious bank robber who tried to run down an FBI agent with his car in Las Vegas in 1960 and was on the agency's most wanted list after escaping from a federal prison in Texas in 1968. Paddock was 7 and the oldest of four children when his father was arrested in connection with a string of Phoenix bank robberies. Benjamin Paddock was in prison for the first three years of his oldest son's life.

The Associated Press contributed to this story.