Las Vegas gunman Stephen Paddock set up multiple surveillance cameras in his hotel room and in the hallway to watch for approaching SWAT teams he knew would ultimately respond to the barrage of gunfire he sprayed into a country music festival Sunday night.

The cameras were part of the meticulous preparation to carry out a massacre that police have uncovered as part of its investigation into Paddock, whose motive for carrying out the attack is still unclear. His shooting spree left 58 dead and more than 500 injured.

In addition to the cameras installed around his hotel room, including at least one hidden in a service cart in the hallway, Paddock had flown his girlfriend out of the country ahead of the attack, according to her family, before making a $100,000 international wire transfer to her.

Authorities found 23 guns in Paddock’s Mandalay Bay Resort hotel room, some mounted on tripods or fitted with scopes, and two “bump stocks,” or accessories that can make a semi-automatic rifle fire in rapid bursts.

“The fact that he had the type of weaponry and the amount of weaponry in that room, it was pre-planned extensively,” Sheriff Joseph Lombardo of Clark County told reporters Tuesday. “I’m pretty sure he evaluated everything that he did in his actions, which is troublesome,” he said, adding that the gunman may have been “radicalized unbeknownst to us.”

After killing 58 people and injuring well over 500, Paddock – a retired accountant and avid gambler who had no known record of criminality, mental illness or political extremism – put the barrel of one of his guns in his own mouth, police say, leaving no clues as to what motivated his carefully-planned rampage.

Investigators hunting for answers in the deadliest mass shooting in modern U.S. history will now focus their attentions on Paddock’s girlfriend, Marilou Danley, after she returned to the U.S. from the Philippines late Tuesday.

Lombardo said detectives had been in contact with the 62-year-old – who flew to the Philippines weeks before the killings and was there at the time of the attack – and anticipated “further information from her shortly.”

He said Danley, an Australian citizen who was reportedly born in the Philippines and lived with Paddock in Mesquite, Nevada, is being treated as “a person of interest” in the inquiry.

Danley, who was filmed being escorted in a wheelchair through Los Angeles International Airport on Tuesday night, is not under arrest, but the FBI hopes she will voluntarily agree to an interview, Reuters reported that, citing a law enforcement source.

High on the list of questions investigators will have for Danley is the nature of the $100,000 wire transfer. Reuters reported that investigators are working off the theory that the money was a form of life insurance payout for Danley, raising questions about how much she knew about Paddock’s plans.

Danley’s sisters, who live on Australia’s Gold Coast, told Australia’s Seven News that Paddock had bought his girlfriend a plane ticket to the Philippines to get her out of the country ahead of the attack.

“She was sent away. She was away so that she will be not there to interfere with what he’s planning,” said one of the sisters, who the network did not identify by name. Danley landed in Manila on Sept. 15, more than two weeks before the attack, making a three-day visit to Hong Kong a week later.

“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’.”

The other sister told the network: “No one can put the puzzles together, no one, except Marilou, because Steve is not here to talk anymore. Only Marilou can maybe help.”

Danley’s return to the U.S. came as authorities released harrowing bodycam footage taken from first responders at the scene of the massacre, as Paddock fired semi-automatic rifles from the vantage point of his hotel room into a crowded music festival below for about ten minutes.

Photographs of Paddock’s hotel room in the aftermath of the assault published by a British newspaper showed the gunman’s body surrounded by a small arsenal of weapons and stacks of ammunition.