He liked to bet big, wagering tens of thousands of dollars in a sitting. He owned homes in four states but preferred staying in casino hotels, sometimes for weeks at a time, as he worked the gambling machines.

He grew up the son of a convicted bank robber who was constantly running from the law. But in his own life, Stephen Paddock, 64, had kept his nose clean until Sunday night, when he suddenly unleashed a firestorm of bullets from his casino hotel room, killing at least 59 people and injuring more than 500 more on the Las Vegas Strip.

“If you told me an asteroid fell into Earth, it would mean the same to me. There's absolutely no sense, no reason he did this,” his brother Eric Paddock said in an interview outside his home in Orlando, Florida. “He's just a guy who played video poker and took cruises and ate burritos at Taco Bell. There's no political affiliation that we know of. There's no religious affiliation that we know of.”

After the shooting, officers found Stephen Paddock dead with 17 guns on the 32nd floor of the Mandalay Bay Resort and Casino, where he had arrived Thursday.

Police believe Paddock acted alone in executing the deadliest mass shooting in modern US history.

Eric Paddock said he knew of five guns his brother kept in his safe but was shocked that a rapid-fire weapon was used in Sunday's shooting.

He said Stephen Paddock didn't hunt and barely shot his guns, once taking Eric's children on a skeet-shooting trip paid for by the casinos.

In the final years of his life, Stephen Paddock was living out his retirement in quiet obscurity. He liked country music, relatives said, and went to concerts like the Route 91 Harvest festival where he killed so many Sunday night.

He was worth more than $2 million, relatives said. Before retiring, he made a small fortune from real estate deals and a business that he and Eric Paddock sold off. He travelled a lot and had millions of free airline miles.

At various points of his life, Stephen Paddock worked for defence contractor Lockheed Martin and as an accountant and property manager. As a retiree, he had no children and plenty of money to play with. So he took up gambling.

“It's like a job for him. It's a job where you make money,” said Eric Paddock, adding that his brother could lose $1 million and still have enough to live on. “He was at the hotel for four months one time. It was like a second home.”

He recalled one time when the entire family took over the top floor of the Atlantis at the casino's expense.

His brother was very particular about the games he played. “It had to be the right machine with double points, and there has to be a contest going on. He won a car one time,” Eric Paddock said.

“He's known. He's a top player. He's the small end of the big fish.”

Over the past two decades, Stephen Paddock had bought and sold properties in several states, including California, Nevada, Florida and Texas, where for a time, neighbours said, he lived with his mother. Public records show Paddock at one point owned two planes and was a licenced pilot. He also had a fishing licence from Alaska.

He told neighbours he was a professional gambler and a prospector, and he appeared to favour buying homes in retirement communities. At one point, he and his longtime girlfriend, Marilou Danley, were living in at least three retirement communities, property records show. Neighbours said the couple seemed almost itinerant, leaving the properties empty for long stretches as Paddock visited his casinos.

Donald Judy, who was his next-door neighbour in Florida until two years ago, said the inside of Paddock's home “looked like a college freshman lived there.” There was no art on the walls and no car in the driveway. Just a dining chair, a bed and two recliners. Paddock was constantly on the move, carrying a suitcase and driving a rental car whenever he stayed at the community near Cocoa Beach.

“It looked like he'd be ready to move at a moment's notice,” Judy said.

Judy said he never flashed his wealth, often wearing khaki cotton pants, with a polo or other collared shirt, and never driving anything nicer than a standard rental car.

A little while after living there, Paddock left Judy a key and asked him to keep an eye on the rarely used house and to borrow any tools he might want. Judy said there were no drugs or parties, nothing unusual except for Paddock's gambling.

“They did seem to always stay up till midnight and sleep in till noon,” Judy said. “They always seemed to stay on Vegas time.”

Then, as quickly as he had appeared, Paddock put up a for-sale sign, Judy said. “He never said much about it, just said they were moving back to Vegas.”

Police in Texas and towns Paddock lived in in Nevada said they could find no records of run-ins with the law involving him.

California records show that Paddock married a woman named Peggy Okamoto in 1985. They divorced in 1990 citing “irreconcilable differences.” In recent years, Danley had become his girlfriend, relatives said.

Authorities said Danley was out of the country at the time of the shooting and was located in Tokyo. She is not considered a suspect.

At one point, Danley worked as a high-limit hostess for Club Paradise, a rewards program in the Atlantis Casino Resort Spa in Reno, Nevada, according to her LinkedIn profile. In a statement, Atlantis officials said she has not worked for the casino for several years.

Diane McKay lived next door to Paddock and Danley at their Reno home until July, when McKay moved away. Danley wasn't forthcoming about her life, and Paddock was unfriendly, McKay recalled. She only saw him in the mornings, when he went to the clubhouse to work out.

“He was weird. Kept to himself,” said McKay, 79. “It was like living next to nothing... You can at least be grumpy, something. He was just nothing, quiet.”

The couple kept their blinds closed, but sometimes Paddock would open the garage door, revealing an enormous safe the size of a refrigerator.

Paddock's father, Benjamin Hoskins Paddock, was on the FBI's Ten Most Wanted list, described on a 1969 wanted poster as “psychopathic'' with suicidal tendencies.

He escaped from prison that year and, according to news accounts, was not captured until 1978, when he was nabbed while running a bingo parlour in Oregon.

Stephen Paddock was the oldest of four boys. Eric, eight years his junior, was the youngest, with two in between: Bruce and Patrick.

Their father died a few years ago, but Eric Paddock grew up thinking their father was already dead. He found out otherwise when Patrick went to the Air Force Academy and was told his father was a decorated veteran and still alive.

“We didn't grow up under his influence,” Eric Paddock said. “I was born on the run in Tucson. My dad was about to be arrested for robbing banks.”

FBI agents interviewed relatives Monday, including Stephen Paddock's mother, who is in her 90s and spoke with him two weeks ago, Eric Paddock said. Five days after Hurricane Irma hit Orlando, Stephen Paddock texted his brother to see whether relatives had been affected.

Eric Paddock said he did not know of any mental illness, alcohol or drug problems in his brother's life. He said he had no clue whether Stephen had gambling debts or was financially troubled.

By Monday night, after an entire day dealing with FBI investigators and reporters camped outside his house, Eric Paddock said he and other relatives were still struggling to process the atrocity carried out by his brother.

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

“When we talked about a month ago, I can't believe he was planning this,” he said, squeezing his eyes closed. “But he must have. It takes time.”

What he knows about his brother doesn't fit with Sunday's massacre of innocents.

“Something broke in his head is the only thing possible. Did he have a stroke?” he said. “I'm hoping they cut open his brain and find something. There's a data point missing.”