The local sheriff described Las Vegas shooter Stephen Paddock as a lone "psychopath."
Investigators were desperately trying to establish the motive of a retired accountant who
killed at least 59 people and wounded more than 500 after amassing
a weapons cache in a hotel room and opening fire on the Las Vegas strip.
As America grappled with the deadliest mass shooting in its history, officials reacted cautiously to an ISIS claim that
Stephen Craig Paddock, 64, had carried out Sunday night's massacre on behalf of the jihadist group.
Police said Paddock, who had no criminal record, smashed windows in his 32nd floor hotel room shortly after 10:00 pm on Sunday and trained bursts of automatic weapons fire on thousands of people attending a country music concert below on the strip.
In video footage of the massacre broadcast on CNN, the rattle of long, sustained gunfire is heard as people scream and scurry for cover. At first they did not not know where the shots were coming from.
"We saw bodies down. We didn't know if they had fallen or had been shot," said Ralph Rodriguez, an IT 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.
ISIS 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."