LAS VEGAS — FBI agents began questioning the Las Vegas gunman's girlfriend on Wednesday for clues to what drove Stephen Paddock to slaughter 59 people from his high-rise hotel suite, a law enforcement official said.

The official said Marilou Danley was interviewed at the bureau's field office in Los Angeles and was with her attorney. The official was not authorized to discuss the investigation publicly and spoke to The Associated Press on condition of anonymity.

Danley, 62, returned to the US on Tuesday night from the Philippines after a weekslong trip abroad.

Three days after the deadliest mass shooting in modern US history, why someone with no known record of violence or crime would open fire on a country music festival was still a mystery.

Sheriff Joseph Lombardo on Tuesday called Danley a "person of interest" in the attack.

A receptionist at the office of Los Angeles-based criminal defense attorney Matthew Lombard confirmed he was representing Danley but would not comment any further.

Paddock, a 64-year-old high-stakes gambler and real estate investor from Mesquite, Nevada, killed himself as police closed in on his 32nd-floor room at the Mandalay Bay hotel casino. More than 500 people were injured in the attack.

Danley's sisters in Australia said in a TV interview there that they believe she couldn't have known about Paddock's murderous plans and that he must have sent her away so she wouldn't interfere.

The sisters — whose faces were obscured and their names withheld — said Danley is "a good person" who would have stopped Paddock had she been there.

"She didn't even know that she was going to the Philippines until Steve said, ‘Marilou, I found you a cheap ticket to the Philippines,'" said one of the sisters, who live near Brisbane.

Meanwhile, US President Donald Trump met privately with victims of the shooting at a Las Vegas hospital Wednesday.

"It's a very sad thing. We are going to pay our respects and to see the police who have done really a fantastic job in a very short time," Trump said before leaving the White House. He said authorities were "learning a lot more" about the gunman.

Whatever Paddock's motive, authorities said he planned the attack methodically, not only stockpiling nearly two dozen guns in his hotel room but setting up cameras in the peephole and on a service cart outside his door, apparently to watch for police closing in on him.

During the rampage, a hotel security guard who approached the room was shot through the door and wounded in the leg.

"The fact that he had the type of weaponry and amount of weaponry in that room, it was preplanned extensively," the sheriff said, "and I'm pretty sure he evaluated everything that he did and his actions, which is troublesome."

FBI Deputy Director Andrew McCabe, speaking at a cybersecurity forum on Wednesday in Boston, said investigators are busy "reconstructing the life, the behavior, the pattern of activity of this individual and anyone and everyone who may have crossed his path in the days and the weeks leading up to this horrific event."

Asked if investigators had determined why Paddock carried out the attack, he said, "We are not there yet.

"This individual and this attack didn't leave the sort of immediately accessible thumbprints that you find on some mass casualty attacks," McCabe said.

Paddock had been stockpiling guns since 1982 and bought 33 of them, mostly rifles, over the past year alone, right up until three days before the attack, Jill Snyder, an agent with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, told CBS on Wednesday.

He had rigged 12 semi-automatic rifles with devices that allowed the guns to fire like an automatic weapon, she said. Authorities previously disclosed that he had such "bump stock" devices with him at the hotel.

Snyder said authorities would not have been notified of the rifle purchases but would have been informed if two or more guns were bought at one time.

Paddock wired $100,000 to the Philippines in the days before the shooting, a US official briefed by law enforcement but not authorized to speak publicly because of the continuing investigation told the AP on condition of anonymity.

Investigators are still trying to trace that money and also are looking into at least a dozen financial reports over the past several weeks that said Paddock gambled more than $10,000 per day, the official said.

AP