MANILA - The girlfriend of a Las Vegas retiree who killed 59 concertgoers is said to be back in the United States to help law enforcement authorities shed light on the mass shooting on Sunday ( Oct 1).

Sources here said Ms Marilou Danley, 62, whom Clark County Sheriff Joseph Lombardo considered a "person of interest" in the investigation on gunman Stephen Paddock, 64, left Manila for Los Angeles on a Philippine Airlines flight on Tuesday local time.

Agents of the US Federal Bureau of Investigation (FBI) were said to have accompanied her.

The New York Times, citing US officials, said she had arrived in the US.

Ms Danley was reportedly born in the Philippines but now holds an Australian passport. She arrived in Manila on Sept 15, and left for Hong Kong on Sept 22. She returned to Manila from Hong Kong on Sept 25.

Immigration officials here declined to release information about her, saying she "is not suspect and appears to have been cleared by police".

Ms Danley and Paddock lived in a condominium at a retirement community in Mesquite, Nevada, about 145km north-east of Las Vegas.

From a high perch at the Mandalay Bay Resort and Casino, Paddock rained a rapid-fire barrage on an outdoor country music concert festival on Sunday night, leaving at least 59 people dead in the bloodiest mass shooting in modern US history. More than 500 people were injured.

Investigators turned their attention to Ms Danley following reports that Paddock wired US$100,000 (S$136,114) to the Philippines. A senior homeland security official told Reuters that investigators assumed the money was intended as a form of life insurance 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.