FBI agents began questioning the Las Vegas gunman’s girlfriend on Wednesday for clues as to what drove Stephen Paddock to slaughter 58 people from his high-rise hotel suite.

Marilou Danley was interviewed at the bureau’s field office in Los Angeles.

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.

Danley, 62, returned to the U.S. on Tuesday night from the Philippines after a weekslong trip abroad. A U.S. official said she was met at Los Angeles International Airport by FBI agents.

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

Clark County Sheriff Joseph Lombardo on Tuesday called Danley a “person of interest” in the attack.

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.

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, said Jill Snyder, an agent with the Federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).

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 handguns were bought at one time.

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.

Danley is an Australian citizen but a native of the Philippines, Pegues reports. She met Paddock after separating from her ex-husband, Geary Danley, in 2013.