Marilou Danley, Stephen Paddock's girlfriend of 64, left Manila on the evening of October 3. US police said that "this woman is the subject of interest in the investigation".
Marilou Danley flew from the Philippines to Los Angeles airport and was picked up by FBI staff for questioning over the shooting in Las Vegas.
According to US sources, Ms. Danley was not arrested, but the FBI hoped she would voluntarily answer the questioning.
A police official in Manila said Danley's trip to the US was "coordinated with the FBI", and she returned to the US to confirm she had no involvement in the bloodiest mass shooting in modern US history.
According to previous reports, the assassin Steven Paddock transferred $100,000 to the Philippines.
The brutal shooting occurred on the night of October 1 during a music festival held in Las Vegas between the airport and the Mandalay Bay casino. Police said Stephen Paddock opened fire from the hotel's 32nd floor and then committed suicide. In Paddock's hotel room, 23 guns of various types were found.
The massacre killed 59 people and injured more than 500 others. This is the largest shooting incident in the US to date.