Adam Housley, Jake Gibson, Brooke Singman and The Associated Press
(Photo by David Becker/Getty Images)

LAS VEGAS – A gunman turned a Las Vegas concert into a killing field Sunday night from his perch on the 32nd floor of the Mandalay Bay Resort and Casino, using at least 10 guns to rain down a steady stream of fire, murdering at least 50 people and injuring more than 400 others in the deadliest mass shooting in modern United States history.

The suspect, who died of a self-inflicted gunshot wound, was identified as 64-year-old Stephen Paddock, a resident of Mesquite, Nevada. Police initially sought a woman believed to be Paddock's roommate, Marilou Danley, as a "person of interest." Detectives later made contact with her, and "do not believe she is involved with the shooting on The Strip."

Clark County Sheriff Joseph Lombardo said an "excess of 10 rifles" were found in the room, but did not immediately reveal a motive. Paddock had been in the hotel room since September 28, according to Lombardo.

Authorities said two on-duty Las Vegas Metropolitan Police Department officers were injured during the shooting. One is in stable condition after surgery, and the other sustained minor injuries. Two off-duty police officers attending the concert were killed.

President Trump tweeted his condolences to the victims of the Las Vegas massacre, saying "My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!"

The gunman, who fired down on the Route 91 Harvest Festival from a room on the 32nd floor of the Mandalay Bay Resort and Casino, died from a self-inflicted gunshot wound just as police made entry to the room, according to LVMPD undersheriff Kevin McMahill.

Federal law enforcement sources told Fox News that Paddock "was known to local authorities" in Vegas, and multiple weapons were found in his hotel room. 

At this time, federal officials do not see any connection to international terrorism and little is known about Paddock's motivation, sources said. 

The gunman's brother, Eric Paddock, told reporters outside his Central Florida home early Monday "an asteroid just fell on us," and said Stephen Paddock has no history of mental illness.

Paddock said his brother is "just a guy" and he "freaked," and had retired to Vegas because he liked gambling.

The Department of Homeland Security said Monday morning that the department is "closely monitoring" and helping partners investigate the tragedy, but at this time has "no information to indicate a specific credible threat involving other public venues in the country."

Attorney General Jeff Sessions spoke with Sheriff Lombardo offering his full support, Department of Justice officials told Fox News.

Authorities first received calls about an active shooting at about 10:08 p.m. Country music star Jason Aldean was performing at the Route 91 Harvest Festival when the gunfire erupted.

Aldean was performing his last song of the night. Initially, those in attendance said they thought the sound was firecrackers. But as the shots continued, Aldean stopped singing and some concertgoers could be heard yelling to each other to get down.

One witness told KSVN that he heard “hundreds of shots.” The gunfire was rapid and reportedly confused with firecrackers.

"It sounded like a machine gun," one vendor told Fox News. "It sounded like more than one machine gun."

Authorities said law enforcement swarmed the hotel and killed the gunman in a room on the 32nd floor. Responding officers used an explosive device to force the door open into the room, law enforcement officials told Fox News.

Country singer Jake Owen, who performed before Aldean, told Fox News the gunfire was "non-stop." 

"You couldn't tell where it was coming from. It was loud and non-stop," he said. 

Some concertgoers stayed behind to offer help to those around them.

“Everybody I saw breathing, I helped,” a concertgoer told Fox News.

Kodiak Yazzie, 36, said the music stopped temporarily and started up again before another round of pops sent the performers ducking for cover and fleeing the stage.

"It was the craziest stuff I've ever seen in my entire life," Yazzie told the Associated Press. "You could hear that the noise was coming from west of us, from Mandalay Bay. You could see a flash- flash- flash- flash."

As the 40,000 fans in the crowd began to flee, Yazzie took cover and said he saw flashes of light coming from the Mandalay Bay hotel tower high above.

Another concertgoer told the Las Vegas Review-Journal the shots sounded like fireworks, and she hid in a sewer. 

“It was a horror show,” Ivetta Saldana told the newspaper. “People were standing around, then they hit the floor.”

Retired FBI special agent and former national FBI spokesman John Iannarelli, who drove past the scene of the event just moments before the shooting took place, told Fox News the massacre was "obviously well-planned." 

Iannarelli added the gunman used “expensive guns and ammunition.” 

Iannarelli noted that FBI and police are going to speak with every friend and relative, and are conducting forensic review of the suspect's computers and phones.

The shooting at the sold-out Route 91 Harvest festival was the worst mass shooting in modern U.S. history. Forty-nine people were killed when a gunman opened fire at the Pulse nightclub in Orlando in June 2016.

Sunday's shooting came more than four months after a suicide bombing at an Ariana Grande concert in Manchester, England, that killed 22 people. Almost 90 people were killed by gunmen inspired by Islamic State terror group at the Bataclan concert hall in Paris during a performance by Eagles of Death Metal in November 2015.

Fox News'  Adam Housley, Jake Gibson, Brooke Singman and The Associated Press contributed to this report

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