LAS VEGAS (CBS/AP) — A gunman on the 32nd floor of a Las Vegas hotel-casino rained heavy fire down on a crowd of over 22,000 at an outdoor country music festival, turning the expanse into a killing ground from which there was little escape. At least 59 people died.

It was the deadliest mass shooting in modern U.S. history. In addition to the dead, at least 527 people were injured, authorities said.

Concertgoers screamed, ran in terror and scrambled for cover Sunday night in an attack that at first sounded like firecrackers to many but turned out to be dozens of bullets in rapid-fire bursts, perhaps from a fully automatic weapon.

SWAT teams using explosives, stormed the gunman’s Mandalay Bay hotel room and found he had killed himself, authorities said.

Investigators say 23 firearms were found in the hotel room and 19 firearms were found inside the home of the now identified shooter, Stephen Craig Paddock, 64, of Mesquite, Nevada.

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There was no immediate word on the motive for the bloodshed.

Clark County Sheriff Joseph Lombardo said authorities believe this was a “lone wolf” attack. And the U.S. Homeland Security Department said there was no “specific credible threat” involving other public venues in the U.S.

“What we are going to try to do as best we can is to get our first responders back on their feet and responding and conducting a proper investigation to ensure that we have the safety of this community at heart,” the sheriff said.

Paddock had checked into the hotel room on Thursday, authorities said.

Eric Paddock, the brother of the alleged gunman, said Stephen Paddock was a multimillionaire real estate investor. He told reporters Monday in Orlando that his brother was also an accountant for many years.

He was not aware of his brother having any recent financial difficulties.

The Associated Press reports that the Islamic State of Iraq and Syria is claiming responsibility for the attack. The terror group claims Stephen Paddock converted to Islam months ago, but provided no evidence.

The FBI says there is no known connection with an international terrorist group.

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Lombardo says he doesn’t know if this shooting could have been prevented.

“This individual was described as a lone wolf, I don’t know how it could have been prevented. We didn’t have any prior knowledge to this individual. It wasn’t evident that he had any weapons in his room. We have determined that there has been employees going to and fro to his room and nothing nefarious was noticed at this point,” explained Lombardo.

President Donald Trump called it an “act of pure evil.”

“To the families of the victims, we are praying for you and we are hear for you and we ask God to help see you through this dark period,” Trump said on Monday morning.

Trump added that he will be visiting Las Vegas on Wednesday.

“In moments of tragedy and horror, America comes together as one and it always has,” said Trump. “We call upon the bonds of citizenship that ties a community and the comfort of our common humanity. Our unity cannot be shattered by evil, our bonds cannot be broken by violence and though we feel such great anger at the senseless murder of our fellow citizens, it is our love that defines us today, and always will, forever.”

He continued, “Even the darkest face can be brightened by a single light, and even the most terrible despair can be illuminated by a single ray of hope.”

In a tweet Monday, Trump offered “My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!”

My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you! — Donald J. Trump (@realDonaldTrump) October 2, 2017

White House Press Secretary Sarah Huckabee Sanders choked up while talking about the shooting during the White House press briefing.

“The memory of those who displayed the ultimate expression of love in the midst of an unimaginable act of hate will never fade,” she said.

.@PressSec: "The memory of those who displayed the ultimate expression of love in the midst of an unimaginable act of hate will never fade." pic.twitter.com/mhEJrFzjJj — CBS News (@CBSNews) October 2, 2017

For families looking to locate missing loved ones, please call 1-866-535-5654. — LVMPD (@LVMPD) October 2, 2017

Pennsylvania Sen. Bob Casey and New Jersey Sen. Cory Booker also expressed their thoughts on the shooting.

Praying for the victims, their families, and all those who responded to this horrific shooting in Las Vegas. — Senator Bob Casey (@SenBobCasey) October 2, 2017

My soul aches over Las Vegas. My prayers are with the victims. And my prayers are with our nation, may we resolve to do more stop such evil. — Cory Booker (@CoryBooker) October 2, 2017

Former Pennsylvania Gov. and the first U.S. Secretary of Homeland Security Tom Ridge issued the following statement:

“In the wake of the unspeakable act of inhumanity in Las Vegas, we are once again reminded of the heroism of our first responders who ran toward the bullets to save lives. These brave men and women find themselves on the front lines when suddenly faced with a lone-wolf attacker hellbent on causing massive casualties. While we mourn the loss of life and pray for the recovery of those wounded, we must remember that, by definition, democracies are soft targets, vulnerable to madmen at home or terrorists from afar. But that should only reinforce our resolve to maintain our freedoms and not cower in the face of such indiscriminate evil.”

Country music star Jason Aldean was performing Sunday night at the end of the three-day Route 91 Harvest Festival when the gunman opened fire across the street from inside the Mandalay Bay Hotel and Casino. SWAT teams using explosives stormed the gunman’s hotel room in the sleek, gold-colored glass skyscraper and found he had killed himself, authorities said. He had as many as 10 guns with him, including rifles, they said.

Our thoughts & prayers are with the victims of last night's tragic events. We’re grateful for the immediate actions of our first responders. pic.twitter.com/Arf8edj1iZ — Mandalay Bay Resort (@MandalayBay) October 2, 2017

Aldean was in the middle of a song when the shots came rapidly: Pop-pop-pop-pop. Video of the shooting then showed Aldean stopping and the crowd getting quiet as if they were unsure of what had just happened. The gunman paused and then fired another volley of muzzle flashes from the gold glass casino as more victims fell to the ground while others fled in panic. Some said they hid behind concession stands and other crawled under parked cars.

Kodiak Yazzie, 36, said the music stopped temporarily when the first shots began and the tune even started up again before the second 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 said. “You could hear that the noise was coming from west of us, from Mandalay Bay. You could see a flash- flash- flash- flash.”

Thousands in the crowd fled as the bullets ran rampant. Monique Dumas from British Columbia, Canada, said she was at the concert, six rows from the front of the stage when she thought she heard a bottle breaking, and then a burst of popping sounds that may have been fireworks. She said as she made her way out, it was “organized chaos” as everyone fled. “It took four to five minutes and all that time there was gunfire.”

In addition to Paddock, police said they located a woman who may have been his roommate — Marilou Danley, 62. Lombardo said they believe this was a “lone wolf” attack.

“It’s a devastating time,” Lombardo said.

‘Beyond Horrific.’ Country Music World Stunned By Las Vegas Shooting

Police shut down the usually busy Las Vegas Boulevard and authorities across the state and federal ranks converged onto the scene as dozens of ambulances ferried those struck by gunfire. Nearby Interstate 15 and flights at McCarran International Airport were also halted. Hospital emergency rooms were jammed with victims delivered by ambulance. Others loaded the wounded into their cars and drove them to hospitals.

Jose Baggett, 31, of Las Vegas, said he and a friend were in the lobby of the Luxor hotel-casino — directly north of the festival — when people began to run, almost like in a stampede. He said people were crying and as he and his friend started walking away minutes later, they encountered police checkpoints where officers were carrying shotguns and assault rifles.

“There were armored personnel vehicles, SWAT vehicles, ambulances, and at least a half-mile of police cars,” Baggett said.

Two on-duty LVMPD officers were injured during the shooting. One is in stable condition after surgery and the other sustained minor injuries — LVMPD (@LVMPD) October 2, 2017

Among those killed were two off-duty police officers who were attending the concert and two other on-duty officers were wounded, including one in critical condition, police said.

Hours after the shooting, Aldean posted on Instagram that he and his crew were safe and said the shooting was “beyond horrific.”

“It hurts my heart that this would happen to anyone who was just coming out to enjoy what should have been a fun night,” Aldean said.

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.

Also in June, The Voice singer Christina Grimmie, of South Jersey, was gunned down by a deranged fan after a concert in Orlando while signing autographs.

Her family released this statement on the Las Vegas shootings:

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 at the Bataclan concert hall in Paris during a performance by Eagles of Death Metal in November 2015.

(TM and © Copyright 2017 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2017 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)