The first photo of a man believed to be Stephen Paddock - the Las Vegas gunman who killed at least 50 people in the worst shooting in US history - has been released.

Paddock reportedly arrived in Las Vegas from his home in Mesquite Thursday, when he checked into a hotel room in the Mandalay Bay Hotel and Casino. He stayed there until Sunday, when he broke his 32nd floor window, and open fired on a crowd at an outdoor country music festival across the street. At least 58 people have been reported dead, and another 515 have been taken to the hospital.

Police did not immediately provide possible motives for why Paddock decided to open fire on concert goers. Paddock's body was found alongside at least eight rifles, which were not noticed by anyone working at the hotel in the days before the attack. House keeping had reportedly entered his room several times, but did not notice anything worrisome. It's not clear if he had the weapons in the room in the days leading up to the attack, or if he had moved them into his room Sunday before the shooting.

In an interview in Florida, Paddock's brother said that he had no idea why is brother would have been pushed to become the worst mass shooter in modern American history. He noted that he had helped his brother to move to Nevada several years ago and that he wasn't aware of his brother owning any assault rifles during that time. He said he was "dumbfounded" by the news that his brother had orchestrated the attack.

"There is no reason we can imagine why Stephen would do something like this," Eric Paddock said. "We have no idea how this happened. It's like an asteroid just fell on top of our family."

Paddock reportedly had a pilot licence, and had worked as an accountant before retiring. People in his 55-plus community in Mesquite appeared to not have a close relationship with Paddock, according to reporters on the ground in Mesquite. He lived there with a live-in girlfriend.

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