'My conscience is clear': Vegas gunman's Aussie girlfriend tells family not to 'worry'

The girlfriend of Las Vegas gunman Stephen Paddock has a “clean conscience” as police investigate the worst mass shooting in modern US history.

Marilou Danley, 62, is being questioned by the FBI as the authorities seek to determine what led her 64-year-old boyfriend to carry out his attack from a window of the Mandalay Bay hotel on Sunday night leaving 59 dead and injuring more than 500.

Ms Danley’s brother, Reynaldo Bustos, said he contacted her not long after the shooting.

"I called her up immediately and she said, 'Relax, we shouldn't worry about it. I'll fix it. Do not panic. I have a clean conscience,'" Bustos told ABC News in the Philippines.

Stephen Paddock killed 59 people at a Las Vegas festival. Source: Supplied

Ms Danley was out of the country when Paddock rained bullets down on concert-goers on the Las Vegas Strip on Sunday night, killing at least 59 and injuring more than 500, and relatives quoted her as saying she knew nothing about his diabolical plan.

Footage shows a wheelchair-bound Ms Danley returned to the United States from the Philippines on Tuesday night and was met by agents of the Federal Bureau of Investigation at Los Angeles airport.

In a statement read by her lawyer just hours after her arrival, she said she she had no idea" whatsoever" that Paddock "was planning violence against anyone".

Ms Danley said she was "devastated by the deaths and injuries that have occurred" and said she prayed for the victims and their families.

Ms Danley reportedly met Paddock through gambling. Source: Facebook

Police have not described Ms Danley, who spent time living on the Gold Coast, as a suspect but Las Vegas Sheriff Joe Lombardo said Tuesday that she was a "person of interest" and law enforcement hoped she could shed some light on the investigation.

According to Australian authorities, the Filipino-born Ms Danley has Australian citizenship and has family there.

Interviewed with her face blurred so she could remain anonymous, one of Danley's sisters told 7 News she believed Paddock had deliberately sent her away.

"I know that she don't know anything as well like us. She was sent away. She was away so that she will be not there to interfere with what he's planning," she said.

No motive has emerged yet for the deadly shooting spree by Paddock, a64-year-old retired accountant, who liked to gamble for high stakes and owned a comfortable home at a golf course retirement community near Las Vegas.

Terrified festival goers duck for cover as gunfire hails down. Source: Getty Images

Mourners pay tribute at a makeshift memorial on the Las Vegas Strip for the victims of the mass shooting. Source: AAP

It was through his gambling that Paddock reportedly met Ms Danley, when she was working as a hostess at a casino in Reno, Nevada, several years ago.

Paddock and Ms Danley shared a home in the town of Mesquite, 130km northeast of Las Vegas, where the authorities found a number of guns while searching the property.

Neighbours have said the couple mostly kept to themselves and were frequently away for weeks at a time on gambling trips.

Mourners attend a candlelight vigil at the corner of Sahara Avenue and Las Vegas Boulevard for the victims of Sunday night's mass shooting. Source: Getty Images

According to ABC News, Ms Danley left the United States for the Philippines on September 15, about two weeks before Paddock checked into his room at the Mandalay Bay hotel and began the final phase of carrying out an attack that the authorities said was meticulously planned.

She is not under arrest or currently facing any charges.

Other reports have said she left the country on September 25.

Ms Danley arrives in Vegas in a wheelchair. Source: 7 News