The brother of the man identified as the gunman in what’s being called the deadliest mass shooting in U.S. history was at a complete loss early Monday to explain what might have precipitated the attack.

Stephen Paddock’s brother, Eric Paddock, who lives in Florida, told the Orlando Sentinel: “We are completely dumbfounded. We can’t understand what happened.”

Stephen Paddock, 64, unleashed bullets onto the Las Vegas street from a 32nd floor room at Mandalay Bay. Many of the victims were enjoying a concert performance by country music star Jason Aldean at the time of the shooting Sunday night.

Officials said in a Monday morning news conference that 58 have been pronounced dead, with 515 injured.

Paddock had checked into the hotel room on Thursday, authorities said. By the time police had identified and approached the room, Paddock had killed himself.

CBS Orlando affiliate tracks down Eric Paddock, Stephen Paddock’s brother – “we’re horrified, shocked, completely dumbfounded” pic.twitter.com/0ZcdtOXGHx

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@JoeHoldenCBS3

In an address to the nation, U.S. President Donald Trump called it “an act of pure evil.”

Sheriff Joseph Lombardo said authorities believe it was a “lone wolf” attack. The U.S. Homeland Security Department said there was no “specific credible threat” involving other public venues in the U.S.

Lombardo said there was no evidence he was linked to a militant group despite the customary claim of responsbility by ISIS following attacks in the West.

“We have no idea what his belief system was,” Lombardo said.

Paddock did not have a criminal record, according to police.

Lombardo said police found “in excess of 10 rifles” in Paddock’s possession, and that all items from the Mandalay Bay room have been seized as part of the investigation.

Residence searched

Eric Paddock said his brother owned guns, but to his knowledge had never drawn one in anger. He said Paddock was a Florida resident before moving to Nevada two years ago.

Stephen Paddock lived in what was described as quiet neighbourhood in Mesquite, Nevada not known for criminal activity. Quinn Everett of Mesquite, Nev., Police also said there were no active threats to local residents in Mesquite.

Everett said Paddock and an adult woman have been confirmed as living at the residence described as a  single family home, but he was unsure if there were additional residents.

It is the latest of unrelated acts of public violence that have stunned residents and visitors in the tourist mecca in the past few years:

• A shooting incident occurred March 27, 2017 on a double-decker bus on Las Vegas Blvd., on March near the Cosmopolitan and Bellagio hotels. A bus passenger stood up and fired several rounds with a handgun, killing one and injuring hours. An hours-long standoff closed major roads before a suspect surrendered. He has been charged with murder.

• A woman was killed and two Quebec residents were among 34 injured on Dec. 20, 2015 between the Paris and Planet Hollywood hotel-casinos after a vehicle climbed sidewalks and struck pedestrians. A trial is set for early 2018 for Lakeisha Holloway, who has been found mentally competent.

• In June 2014, a young married couple known for extreme anti-government views shot and killed two police officers who were taking a break at a Las Vegas pizzeria. Another man was killed by the couple subsequently at a local Wal-Mart. Jerad Miller was killed in a shootout with police while his wife Amanda fatally shot herself.