Stephen Paddock, the man behind one of the deadliest mass shootings in the U.S. history, was a millionaire, NBC News reported Friday. Paddock opened fire on a crowd of people gathered on the Las Vegas Strip for a music festival, killing 58 people and leaving hundreds injured.

According to the Internal Revenue Service (IRS), Paddock earned at least $5 million in 2015, NBC News reported. The IRS is the revenue service of the United States federal government.

Paddock owned various properties in four states, however, the 64-year-old preferred staying at casino hotels for weeks at a stretch, the Independent reported. The report also stated that Paddock also made a small fortune from his real estate business besides gambling.

In an interview outside his home in Orlando, Florida, Paddock’s brother, Eric said: “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.”

“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. Something had to happen to Steve – I'm not even trying to excuse it – but something happened that drove him into the pit of hell and he did this,” he added.

Speaking further about Paddock’s gambling business, Eric said: “It's like a job for him. It's a job where you make money. He was at the hotel for four months one time. It was like a second home.”

Eric also said that even if Paddock lost $1 million in gambling, he would still have enough money to survive.

Meanwhile, several theories about Paddock’s “disturbed” and “dangerous” past surfaced. Paddock’s girlfriend Marilou Danley said she was shocked by Paddock’s crime. “I am devastated by the deaths and the injuries that have occurred and my prayers go out to the victims and their families and all those who have been hurt by these awful events,” her statement read.

“I have faith in God and I will continue to pray for everyone who has been harmed or hurt. I'm a mother and a grandmother and my heart breaks for all who have lost loved ones. He [Paddock] never said anything to me or took any action, that I was aware of, that I understood in any way to be a warning that something horrible like this was going to happen,” she added.

Danley also recalled how Paddock might have suffered from mental anguish and that how he lay in bed screaming.

Recalling his encounter with Paddock, his neighbor Diane Mckay said: “He was weird. Kept to himself. It was like living next to nothing... You can at least be grumpy, something. He was just nothing, quiet.”