At least 58 people are dead and 500 others injured after gunfire broke out at a country music festival in Las Vegas, authorities said early Monday, in what is the deadliest mass shooting in U.S. history.

Sheriff Joe Lombardo told reporters that the suspect, identified as Stephen Paddock, 64, fired on the crowd at an outdoor concert from the 32nd floor of the Mandalay Bay hotel.

Paddock, a Mesquite, Nev., resident, was found dead in his room when officers breached its door, Lombardo said. Smoke from the gunfire reportedly set off an alarm in that room. 

Authorities are searching Paddock's room and his home, he added.

Officials in Mesquite told CBS News that they had had no run-ins with Paddock. 

Lombardo also said authorities believe they have located Marilou Danley, who was initially described as Paddock's roommate or companion. The woman is no longer considered a "person of interest," the The Associated Press reported, and is not believed to have been involved in the attack.

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The FBI said on Monday that its investigation had turned up no "connection with an international terrorist group."

Shots were fired while Jason Aldean was performing at the end of the three-day Route 91 Harvest Festival, which reportedly drew 30,000 attendees. Aldean was rushed off stage and said later in an Instagram post that he is safe. He called the attack "beyond horrific." 

Two off-duty members of the Los Angeles Sheriff's Department were reportedly shot during the attack, according to the AP. One is in critical condition and the other is in stable condition.

Sen. Dean HellerDean Arthur HellerTrump suggests Heller lost reelection bid because he was 'hostile' during 2016 presidential campaign Trump picks ex-oil lobbyist David Bernhardt for Interior secretary Oregon Dem top recipient of 2018 marijuana industry money, study finds MORE (R-Nev.) said the attack was a "senseless, horrifying act of violence" and thanked police and first responders.

"Senseless, horrifying act of violence in Las Vegas tonight. Praying for all the victims & those impacted by the tragedy," Heller tweeted.

Nevada Gov. Brian Sandoval (R) also tweeted that his prayers are with those affected by the violence.

"A tragic & heinous act of violence has shaken the #Nevada family," he tweeted. "Our prayers are w/ the victims & all affected by this act of cowardice."

This breaking news report was last updated at 12:02 p.m.