Las Vegas gunman's girlfriend officially 'person of interest,' as she arrives back in the United States.

A terrorism link to the Philippines has not been ruled out as the inspiration for the Las Vegas concert massacre as the gunman’s Filipina-Australian girlfriend arrives back in the US.

Marilou Danley, accompanied by FBI agents, arrived in Los Angeles on Tuesday night (Wednesday AEDT) on a flight from Manila and was met by FBI agents. She will later be taken to Las Vegas.

Investigators want to know why her boyfriend Stephen Paddock, 64, meticulously planned and then executed a sniper attack from the 32nd floor of his suite in the Mandalay Bay casino that killed 59 concertgoers and injured more than 500 others on Sunday.

Danley, an Australian citizen born in the Philippines, had been sharing Paddock’s home at a retirement community in Mesquite, Nevada, 130km northeast of Las Vegas, according to public records.

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“We have a lot of questions, I can tell you that,” Las Vegas Undersheriff Kevin McMahill told reporters on Tuesday.

At an earlier briefing, Sherrif Joseph Lombardo reiterated police had no other suspects in the shooting itself.

Investigators initially distanced Paddock’s murderous rampage from terrorism but with the lack of a motive, Ms Danley’s presence in the Philippines and reports Paddock wired $US100,000 ($A127,600) to the terrorism hot spot, authorities refused to rule it out.

“We haven’t absolutely ruled out anything in this investigation,” said Undersheriff McMahill when asked about a potential Philippines terrorism link.

“We have a lot more questions than we have answers today.”

However, a senior US homeland security official, who has been briefed regularly on the probe but spoke on condition of anonymity, said the working assumption of investigators was the money was intended as a form of life insurance payment for Ms Danley.

The official said US authorities were eager to question Ms Danley, who described herself on social media websites as a “casino professional”, mother and grandmother, about whether Paddock encouraged her to leave the US before he went on his rampage.

Undersheriff McMahill said the FBI had financial subpoenas to determine Paddock’s money movement.

Las Vegas Sheriff Joseph Lombardo told reporters earlier on Tuesday that Ms Danley was “a person of interest” and her US arrival meant a “substantial amount” of information on Paddock’s potential motives would emerge in the next 48 hours.

Forty-seven firearms were recovered from three locations searched by investigators – Paddock’s hotel suite, his home in Mesquite and another property associated with him in Reno, Nevada.

Ms Danley moved in the early 1980s from the Philippines to Queensland where she lived for around 10 years and took out Australian citizenship before moving to the US, where she worked at casinos.

Her nephew Jordan Knights in Brisbane said he met Paddock on a recent trip to Las Vegas with his mother.

“Didn’t seem like the type of guy that could do that,” Mr Knights told the Nine Network..

“I didn’t even know he knew about guns.”