Authorities investigating the Las Vegas massacre are reportedly seeking information on a second woman seen with assailant Stephen Paddock.

Police have said that the killer acted alone when he rained down bullets on a country music concert from his room at the Mandalay Bay Hotel, killing 59 and injuring 489.

They have questioned Paddock’s girlfriend, Marilou Danley, but have said she is not a suspect.

However, investigators have broadened their inquiry and are hoping to learn more about a woman spotted with him in the days before he opened fire, according to NBC News. The Las Vegas Metropolitan Police Department did not immediately respond to The Independent’s request for comment.

Citing anonymous law enforcement officials, NBC News reported that investigators are seeking the mystery woman to help them construct a timeline of the days leading up to the attack.

Some details of that timeline have already emerged. Officials have sketched out how Paddock methodically prepared for days after checking into his room, which had sweeping view over the concert ground.

There he stockpiled guns and set up a surveillance system. A raid of his home in a retirement community uncovered another armoury of firearms, ammunition and explosives.

Labelled a “person of interest” by authorities, Ms Danley returned to America from the Philippines yesterday and was questioned by the FBI.

Las Vegas shooting – in pictures Show all 15 1 /15 Las Vegas shooting – in pictures Las Vegas shooting – in pictures People scramble for shelter at the Route 91 Harvest country music festival after gun fire was heard Getty Las Vegas shooting – in pictures People carry a person at the Route 91 Harvest country music festival after shots were fired David Becker/Getty Las Vegas shooting – in pictures People run from the Route 91 Harvest country music festival after gun fire was heard David Becker/Getty Las Vegas shooting – in pictures A handout photo released via Twitter by Eiki Hrafnsson (@EirikurH) showing concertgoers running away from the scene (C) after shots range out at the Route 91 Harvest festival on Las Vegas Boulevard EPA/Eiki Hrafnsson Las Vegas shooting – in pictures People lie on the ground at the Route 91 Harvest country music festival after hearing gun fire Getty Las Vegas shooting – in pictures A man in a wheelchair is taken away from the Route 91 Harvest country music festival after hearing gun fire David Becker/Getty Las Vegas shooting – in pictures People stand on the street outside the Mandalay Bay hotel near the scene of the Route 91 Harvest festival on Las Vegas Boulevard EPA/Paul Buck Las Vegas shooting – in pictures FBI agents confer in front of the Tropicana hotel-casino after a mass shooting during a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Las Vegas police run by a banner on the fence at the Route 91 Harvest country music festival grounds after shots were fired David Becker/Getty Las Vegas shooting – in pictures An injured person is tended to in the intersection of Tropicana Ave. and Las Vegas Boulevard after a mass shooting at a country music festival Ethan Miller/Getty Las Vegas shooting – in pictures Metro Police officers pass by the front of the Tropicana hotel-casino after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures A woman sits on a curb at the scene of a shooting outside of a music festival along the Las Vegas Strip AP/John Locher Las Vegas shooting – in pictures A cowboy hat lays in the street after shots were fired near a country music festival in Las Vegas Getty Las Vegas shooting – in pictures Las Vegas Metro Police and medical workers stage in the intersection of Tropicana Avenue and Las Vegas Boulevard South after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Sheriff Joe Lombardo (2-R) speaking during a press briefing in the aftermath of the active shooter incident on Las Vegas Boulevard EPA

She released a statement through her attorney disavowing any knowledge of Mr Paddock’s plot.

“I knew Stephen as a kind, caring, quiet man,” her statement.