The brother of Stephen Paddock, who shot and killed 59 people and wounded more than 500 others at a country music festival in Las Vegas, said he can't fathom what would've driven his brother to rain gunfire down on concert-goers Sunday night and said he hopes an autopsy shows Stephen Paddock had a brain tumor.

Speaking to reporters outside his home in Orlando, Fla., Eric Paddock expressed dismay and confusion as to why his brother would've fired down at a crowd of 22,000 attendees of the Route 91 Harvest music festival.

"When Steve can do this, we are in deep shit because there's just nothing there," Eric Paddock said Tuesday. "You find me where someone whose like Steve does this. I hope to hell they find when they do an autopsy that there's a tumor in his head or something, because if they don't, we're all in trouble."

Eric Paddock described his brother as "highly intelligent," and someone who didn't accept help from others. Rather, the 64-year-old was a "standalone guy" who gambled a lot, and viewed the casino less as a place for entertainment, and more as a job.

Stephen Paddock opened fire on attendees of the Route 91 music festival from a hotel room located on the 32nd floor of the Mandalay Bay Hotel and Casino, where he had been staying since Sept. 28. He killed himself before law enforcement could breach the room.

Police found at least 23 weapons in Stephen Paddock's suite at the Mandalay Bay. Sheriff Joe Lombardo of the Las Vegas Metropolitan Police Department said the gunman brought at least 10 suitcases into his room.

At least one of the rifles was outfitted with a "bump stock," a device used to convert a semi-automatic firearm to fully automatic.

Officers also found 19 guns at Stephen Paddock's house in Mesquite, Nev.

One week before the mass shooting, Stephen Paddock wired $100,000 to an account in the Philippines, the home country of his live-in girlfriend, Marilou Danley, according to NBC News.

Danley, 62, traveled to Hong Kong on Sept. 25, and is scheduled to arrive back in the United States on Wednesday. It's unclear whether the wired money was intended for her.

Eric Paddock said his brother was the type of person who took care of the people he loved, including Danley, and said it's likely he intentionally made sure his girlfriend was out of the country when he carried out the attack to protect her.

But Eric Paddock said he can't reconcile how a man who wanted to make sure his girlfriend was safe could take the lives of so many others.

"My heart is torn—is destroyed for all these people, but I can't tell you why Steve did what he did. It's so far over the side of the cliff from Steve that I knew," Eric Paddock said. "…The fact that he took care of Marilou and killed all those people, there's just no connection there for me. I don't understand how Steve got to that point."

Eric Paddock said his brother was wealthy and worked as an accountant.

Lockheed Martin confirmed Monday the 64-year-old worked for a predecessor company of the defense giant for three years during the 1980s, and the Associated Press reported Tuesday that Stephen Paddock worked as a letter carrier and an IRS agent for close to 10 years during the 1970s and 1980s.