The lone gunman in Sunday night’s shooting that left 59 people dead in Las Vegas was the son of a notorious bank robber and had no criminal history in Nevada, according to authorities.

The gunman has been identified as 64-year-old Stephen Craig Paddock, of Mesquite, Nev., a town about an hour northeast of Las Vegas, where he lived in an apartment with a 62-year-old girlfriend.

Reporters asked Las Vegas Police Sheriff Joseph Lombardo Monday morning about the suspected motive for the attack. He responded: "I can't get into the mind of a psychopath at this point." He added that a check of federal and state databases showed Paddock was simply not on law enforcement authorities' radar.

Man of ‘substantial wealth’

Paddock’s brother, Eric Paddock, who lives in Orlando, Fla., spoke with reporters outside his home and told them he was stunned by the shooting, saying there had never been anything to indicate his brother might engage in such an attack.

He said his brother “was just a guy” and seemed to have no political leanings of any kind.

"No affiliation, no religion, no politics. He never cared about any of that stuff," he said. "He was a guy who had money. He went on cruises and gambled."

Eric Paddock told The Associated Press that he had not talked to his brother in six months and last heard from him when Stephen checked in by text message after Hurricane Irma.

He also said his brother was a multimillionaire. "He had substantial wealth. He'd tell me when he'd win. He'd grouse when he'd lost. He never said he'd lost four million dollars or something. I think he would have told me."

Paddock added that several of his family members had been speaking with Las Vegas police to try to assist in their investigation.

Father was a bank robber

Eric Paddock confirmed to The Orlando Sentinel that their father was Benjamin Hoskins Paddock, a bank robber who tried to run down an FBI agent with his car in Las Vegas in 1960 and wound up on the agency's most wanted list after escaping from a federal prison in Texas in 1968.

Stephen Paddock was seven at the time of the robberies. Neighbour Eva Price told the Tucson Citizen that she was “trying to keep Steve from knowing his father is held as a bank robber,” adding, “I hardly know the family, but Steve is a nice boy. It's a terrible thing."

An FBI poster issued after the escape said Benjamin Hoskins Paddock had been "diagnosed as psychopathic" and should be considered "armed and very dangerous." He was caught in 1978 and died in 1998. Stephen Paddock later bought his house in Mesquite.

ISIS claim doubted

ISIS tried to claim responsibility for the attack, saying the gunman was "a soldier" who had converted to Islam months ago. The FBI disputed that claim, saying there's no evidence the shooter had connections to any terrorist group.

The CIA as well, advised caution on "jumping to conclusions" following ISIS’s claim of responsibility.

It’s believed Paddock checked into a room on the 32nd floor of the Mandalay Bay Hotel and Casino on Thursday. On Sunday night, just after 10 p.m. local time, he began shooting from the window of his room at a crowd gathered for a music festival across the street.

SWAT teams from the Las Vegas police were able to “breach” Paddock’s room and found him dead. Police located as many as 10 guns in his room.

While the motive for the shooting remains unclear, Lombardo said this was likely a "lone wolf" attack and it appears the gunman was not connected to any militant group.

“We have no idea what his belief system was,” Lombardo told reporters Monday morning.

Earlier Monday morning, heavily armed police began searching Paddock’s home, which is located in a Nevada retirement community.

Mesquite Police Chief Troy Tanner says police surrounded and entered the three-bedroom home Paddock shared with 62-year-old Marilou Danley.

Earlier, authorities had been searching for Danley, calling her a “person of interest.” They later said they had learned she is out of the country. Lombardo said authorities would try to speak with her when she returns to the United States.

With reports from The Associated Press