As America copes with a mass-shooting in Sin City, the shooter's girlfriend Marilou Danley returns to the US, in a case that has baffled investigators for the lack of an apparent motive.

Flowers are placed near the scene of a mass shooting at a music festival near the Mandalay Bay resort and casino in remembrance of the victims lost and those hurt by the massacre. October 2, 2017.
Flowers are placed near the scene of a mass shooting at a music festival near the Mandalay Bay resort and casino in remembrance of the victims lost and those hurt by the massacre. October 2, 2017. (AP)

Las Vegas gunman Stephen Paddock's girlfriend, 62-year-old Marilou Danley, arrived from the Philippines in Los Angeles on Wednesday where FBI agents will question her about the massacre.

Australian citizen Danley, who US authorities have described as a "person of interest" in the investigation, left Manila, Philippines on Tuesday. 

She had arrived in Manila on September 15, flew to Hong Kong on the 22nd and returned to the Philippines on the 25th.

The police official in Manila said Danley's trip back to the United States "was coordinated with FBI authorities" and that she was returning to clear her name of any involvement in the deadly mass shooting.

The US source said Danley was not under arrest, but that the FBI hoped she would consent to be interviewed voluntarily.

US authorities are eager to question Danley about whether Paddock encouraged her to leave the country before going on his rampage.

Police say massacre was meticulously planned

The Las Vegas gunman transferred $100,000 overseas in the days before the attack and planned the massacre so meticulously that he even set up cameras inside his high-rise hotel room and on a service cart outside his door, apparently to spot anyone coming for him, authorities said on Tuesday.

Meanwhile, investigators are taking a harder look at the shooter's girlfriend and what she might have known about the attack, with the sheriff Joseph Lombardo naming her a "person of interest".

Authorities are trying to determine why Paddock killed 59 people at a country music festival in the deadliest mass shooting in modern US history.

Money transaction

Lombardo said he is "absolutely" confident authorities will find out what set off Paddock, a 64-year-old high-stakes gambler and retired accountant who killed himself before police stormed his 32nd-floor room.

Investigators are also examining a $100,000 wire transfer that Paddock sent to an account in the Philippines that appeared to be intended for Danley, a senior US homeland security official said on Tuesday.

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

The cameras Paddock set up at the Mandalay Bay hotel casino were part of his extensive preparations that included stockpiling nearly two dozen guns in his room before opening fire on the concert below.

"I anticipate he was looking for anybody coming to take him into custody," Lombardo said.

Dozens of guns

During the Sunday night 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."

Lombardo said the investigation is proceeding cautiously in case criminal charges are warranted against someone else.

"This investigation is not ended with the demise of Mr Paddock," the sheriff said.

"Did this person get radicalised unbeknownst to us? And we want to identify that source."

In addition to the cameras, investigators found a computer and 23 guns with him at the hotel, along with "bump stock" devices that can enable a rifle to fire continuously, like an automatic weapon, authorities said.

Nineteen more guns were found at Paddock's Mesquite home and seven at his Reno house.

Video shot outside the broken door of the room show an assault-style rifle with a scope on a bipod.

The sheriff said an internal investigation has been launched to find out how that footage was obtained.

Source: TRTWorld and agencies