Stephen Craig Paddock, the man police have identified as the Las Vegas gunman, was a quiet man with no criminal record or reports of erratic behavior before the shooting.

He was found dead in his hotel room after the shooting.

He checked into a hotel room with his girlfriend's identification, police said, but she was found outside of the country and is not suspected to have played a role in the attack.

Authorities discovered 10 rifles in Paddock's hotel room when they entered.

Paddock's brother, Eric, said he was "not an avid gun guy at all" and has no military background.

The shooter's late father, Benjamin Hoskins Paddock, was on the FBI's Ten Most Wanted list from 1969-1977 and was a diagnosed psychopath.

The Las Vegas police on Monday identified Stephen Craig Paddock as the man who opened fire from the 32nd floor of the Mandalay Bay Resort and Casino with what appeared to be at least one automatic rifle, killing more than 50 and injuring at least 515 others to local hospitals in the deadliest mass shooting in modern US history.

The 64-year-old from Mesquite, Nevada, targeted concertgoers at the Route 91 Harvest country music festival at about 10 p.m. PDT on Sunday, police said. They said Paddock had checked into his hotel room Thursday.

Video and pictures from the festival captured the chaos and increasing panic as extended bursts of rifle fire rang out.

Eric Paddock, the shooter's brother, told CBS News that Stephen was "not an avid gun guy at all."

"The fact that he had those kind of weapons is ... just ... where the hell did he get automatic weapons? He has no military background or anything like that," Eric Paddock said. "He's a guy who lived in a house in Mesquite and drove down and gambled in Las Vegas."

CNN runs a picture of Stephen Paddock, the Las Vegas shooter. CNN

Paddock was retired and had no criminal record before the attack, Reuters reports. He used to work as an accountant, and his brother described him to CNN as "a wealthy guy playing video poker ... on cruises."

A Washington Post report characterized Paddock as a quiet man who occasionally came to Las Vegas to gamble or catch concerts, was a former resident of Texas, and held a hunting license in Alaska.

Paddock was divorced, according to CNN, and his ex-wife resides in Los Angeles. The two divorced 27 years ago after a six-year marriage and have not been in contact in years, the report said.

Paddock had been checked into in his Mandalay Bay hotel room on with his girlfriend's identification for three days before the attack. Police initially identified her as a person of interest but have said she is not a suspect in the attack.

Benjamin Hoskins Paddock, the shooter's father, was a well-known bank robber and on the FBI's Ten Most Wanted list from 1969 to 1977, CNN reported.

Benjamin Hoskins Paddock was a diagnosed psychopath, according to the FBI, and he was convicted of "bank robbery, automobile larceny, and confidence game."

Eric Paddock said he died several years ago.

The bureau's poster on the elder Paddock cautioned that he had committed armed robberies before, had "suicidal tendencies," and "should be considered armed and very dangerous."

His son, Stephen, had at least 10 rifles in the hotel room on the Mandalay Bay's 32nd floor, where he had been staying since September 28, said Joseph Lombardo, the sheriff of the Las Vegas Metropolitan Police Department.

Paddock owned two aircraft and held a pilot's license, according to the "Today" show. Paddock had worked for a predecessor company of Lockheed Martin, the giant defense contractor that builds planes.

Paddock lived in the suburbs around Mesquite, Nevada, which sits near the border with Arizona about an hour and a half from where the shooting took place, the police said. Authorities searched his home on Monday and recovered weapons and ammunition. Paddock had purchased several firearms from California in the past, but none of them were among the weapons found in his hotel room after the shooting, CNN reported.

"We have no idea what his belief system was," Lombardo told reporters. In a subsequent press conference, Lombardo said "I can't get into the mind of a psychopath at this point."

The Daily Mail quoted Paddock's brother Eric as saying he and his mother were "in shock" and "dumbfounded" after finding out about the shooting. According to the Daily Mail, Eric Paddock described his brother as a normal guy who must have "snapped."