04/10/2017 10:30 AM AEDT | Updated 06/10/2017 4:27 PM AEDT

Las Vegas Massacre: Police to Grill Australian Marilou Danley

Police want insight into the motives of killer Stephen Paddock.

Australian citizen Marilou Danley was believed to be either visiting family in the Philippines or with friends in Tokyo when her boyfriend either killed or injured almost 600 people.

The Australian girlfriend of Las Vegas shooter Stephen Paddock has been ordered back to the U.S. to face a grilling from police, as the search for answers to America's deadliest mass shooting continues.

Marilou Danley is expected to return to the U.S. from the Philippines on Wednesday, just days after Paddock killed 59 and left 527 injured when he opened fire on concert-goers from the 32nd floor of a hotel.

Police named Australian citizen Danley -- who it is understood hasn't lived in Australia for 20 years -- as a person of interest shortly after the shooting amid reports Paddock used Danley's ID before the killing.

Paddock brought 23 guns with him to the Mandalay Bay casino, and police also want to talk to Danley about the 23 additional guns found in Paddock's home, which is it thought she shared.

"We anticipate some information from her shortly," Clark County Sheriff Joe Lombardo said.

"She is currently a person of interest."

Paddock wired $100,000 to an account in his live-in girlfriend's home country, the Philippines, a week before he opened fire on unsuspecting revellers.

Reports have also emerged Paddock was verbally abusive to Danley, with employees of a Casino Starbucks telling the The Los Angeles Times he would treat her with a 'mean attitude'.

"He would glare down at her and say -- with a mean attitude -- 'You don't need (a) casino card for this. I'm paying for your drink, just like I'm paying for you'," the employee said.

"Then she would softly say, 'OK' and step back behind him. He was so rude to her in front of us."

A visibly shocked Eric Paddock said on Tuesday he was "horrified" and "dumbfounded" after hearing news about his older brother's murderous rampage.

He described Danley as a "nice lady."

"I've met her three or four times," he said.

"She's got a Facebook page. She sends cookies to my mom."

A neighbour described Danley as "very quiet," and it is believed she had worked for the Atlantis Casino Resort Spa between 2010 and 2013.