The death toll from the deadliest mass shooting in US history rose to 58 on Monday as officials reacted cautiously to an Islamic State claim of responsibility for the massacre at a concert on the Las Vegas Strip.
Police said Stephen Craig Paddock, 64, a wealthy former accountant, smashed windows in his 32nd floor hotel room Sunday night and trained bursts of automatic weapons fire on concert-goers below.
Country music star Jason Aldean rushed off stage when the shooting began shortly after 10:00 pm and fans scattered in panic, desperately seeking cover as bullets rained down from above.
"We saw bodies down. We didn't know if they had fallen or had been shot," said Ralph Rodriguez, an information technology consultant from the Pomona Valley, near Los Angeles, who was at the concert with a group of friends.
"People started grabbing their loved-ones and just strangers, and trying to help them get out of the way," Rodriguez said.
The Islamic State group claimed that Paddock was one of its "soldiers" but the FBI said it had found no such connection so far and the local sheriff described him as a lone "psychopath."
Police said Paddock, who had no criminal record, killed himself before a SWAT team breached his room in the Mandalay Bay hotel overlooking the venue for the country music concert.
President Donald Trump denounced what he called "an act of pure evil" and said he would visit Las Vegas on Wednesday.
But the White House said it would be "premature" to reopen the US debate on tighter gun controls in the wake of the shooting.
"A motive is yet to be determined and it would be premature for us to discuss policy when we don't fully know all of the facts or what took place last night," White House spokeswoman Sarah Sanders said.
Las Vegas Sheriff Joseph Lombardo told reporters at least eight rifles had been recovered from the gunman's hotel room.
Lombardo said Paddock did not appear to have been in any trouble with the law previously.
"This individual is a lone wolf and I don't know how it could have been prevented," he said, declining to speculate as to a motive.
"I can't get into the mind of a psychopath at this point," he said.
Lombardo said Paddock had apparently used some kind of hammer to smash the window of his hotel room before opening fire on the concert crowd of some 22,000 people.
Lombardo said 58 people had been confirmed dead and 515 injured and he said the toll could rise. The authorities issued an appeal for blood donors.
IS described Paddock as a "soldier of the caliphate," saying he converted to Islam several months ago and went by the nom de guerre Abu Abdel Bar al-Amriki -- "The American."
The group provided no evidence to back up its claims and the Federal Bureau of Investigation said it had found no such link so far.
"We have determined to this point no connection with an international terrorist group," FBI special agent Aaron Rouse said.
CIA spokesman Jonathan Liu said "the Intelligence Community is aware of the claim of responsibility by a foreign terrorist organization."
"We advise caution on jumping to conclusions before the facts are in," Liu said.
Paddock, who photographs showed as a greying man with a trimmed beard and moustache, was a former accountant and a licensed private pilot, according to ABC News.
Eric Paddock, the gunman's brother, said he was at a complete loss to understand what may have motivated the shooting.
"This is an asteroid falling out of the sky," he told CBS News, saying his brother had "no religious affiliation, no political affiliation."
"He was my brother. He was a guy. He gambled," Eric Paddock said.
He said his brother was wealthy, had no history of mental illness and was "not an avid gun guy at all."
The brothers grew up in a broken home, according to Eric Paddock. Their estranged father, Patrick Benjamin Paddock, was a violent bank robber jailed in the early 1960s for a series of heists.
Paddock resided in a new golf course development in the desert just outside Mesquite, Nevada, 80 miles northeast (130 kilometers) of Las Vegas.
Witnesses said Paddock opened fire with an initial long burst of gunfire, and appeared to reload as he continued his spree.
Robert Hayes, a firefighter from Los Angeles, said he first thought the shots were some kind of equipment malfunction.
Once he realized what was going on, he joined the first responders, donning one of their vests.
"It was pretty much like a war scene inside," he said.
Emergency crews used anything to hand as makeshift stretchers, including tables and metal railings.
Asked if he thought it was an inexperienced gunman, Hayes said: "With 30,000 people in the arena area, it was kind of like shooting goldfish ... He didn't have to be good."
The Las Vegas attack is the deadliest shooting in recent US history, exceeding the toll of 49 dead in an attack on the Pulse nightclub in Orlando, Florida in June 2016.
Twenty-two people were killed after an Ariana Grande concert in Manchester, England in May when a suicide bomber detonated a nail bomb in the foyer.
Ninety people were killed in November 2015 at the Bataclan in Paris during a concert by US band the Eagles of Death Metal.
Pope Francis said he was "deeply saddened" by the "senseless tragedy" in Las Vegas while Britain's Prime Minister Theresa May called it an "appalling
Russian President Vladimir Putin expressed his condolences in a message to Trump.
"The crime that has taken the lives of tens of peaceful civilians is shocking in its cruelty," Putin said.