Las Vegas shooting: What we know about suspect Stephen Paddock Police engaged the suspect, who is now dead.

 -- Stephen Paddock, a 64-year-old resident of Mesquite, Nevada, is the man suspected of killing at least 59 people and injuring at least 527 others in Las Vegas on Sunday night in what is believed to be the worst mass shooting in modern U.S. history, but his motives remain a mystery.

The shooter opened fire from the 32nd floor of the Mandalay Bay Resort and Casino at a crowd of more than 20,000 concertgoers across the street attending the final night of the Route 91 Harvest Music Festival. Witnesses described the shooting as nonstop gunfire, suggesting the use of automatic or semiautomatic weapons.

Police responded to the scene, breached the suspect’s hotel room and found that the shooter, who they believe acted alone, had already killed himself. Two sources familiar with the investigation said police found about 20 weapons — a mix of rifles and handguns — in Paddock’s hotel room.

Investigators are scouring Paddock’s home for clues to what sparked the deadly rampage. They executed a search warrant using a robot to remove the garage door of his residence, where they found additional weapons and ammunition.

But police said Paddock had no criminal history, save for a minor citation, so officials had no prior knowledge of his activities.

“We checked the federal and local databases and state databases,” said Sheriff Joseph Lombardo, the head of the Las Vegas Metropolitan Police Department. “We had no knowledge of this individual.”

Eric Paddock, the suspected shooter’s brother, told ABC News that the family was completely “dumbstruck” by the news, likening the revelation to being “crushed by an asteroid.”

“We have no idea how or why this happened,” Eric Paddock said. “As far as we know, Steve was perfectly fine.”

He added that his brother was not a man of strong political convictions.

“Steve had nothing to do with any political organization, religious organization, no white supremacist, nothing,” Eric Paddock said.

And while ISIS claimed responsibility for the attack, the FBI has not uncovered any connections between the suspect and any foreign terrorist groups.

“The FBI stated there is no apparent tie to international terrorism,” one senior official told ABC News. “Perhaps ISIS is just trying to take credit.”

Yet for some reason, Stephen Paddock apparently checked into his Las Vegas hotel room last Thursday on a well-planned mission to kill, assembling a remarkable arsenal of firearms. Authorities believe the shooter took the weapons into the hotel on his own and used “a device similar to a hammer” to smash the windows between him and the crowds below.

Authorities are hoping Paddock’s girlfriend, Marilou Danley, 62, who appears to have lived with him in Mesquite and once worked as a casino hostess for high-end players, can provide some insight. She is currently believed to be overseas and is expected to return to the U.S. soon. According to multiple law enforcement sources, however, Paddock has sent tens of thousands of dollars to someone in the Philippines in recent months.

His history offers few hints of violence in his future. A spokesperson for the Office of Personnel Management confirmed to ABC News that Paddock was employed by the federal government from 1975 to 1985, first as a letter carrier for the U.S. Postal Service, then as an agent for the Internal Revenue Service and finally as an auditor for the Defense Contract Audit Agency.

He also worked for a company that later become Lockheed Martin, one of the world’s largest defense contractors.

“Stephen Paddock worked for a predecessor company of Lockheed Martin from 1985 until 1988,” the company told ABC in a statement. “We’re cooperating with authorities to answer questions they may have about Mr. Paddock and his time with the company.”

He was also a pilot who owned an aircraft that he kept at Mesquite Metro Airport in Texas from 2007 to 2009.

“I do not recall that he was ever a person who created any problems for us,” the airport’s director told ABC News. “He kept his accounts up to date, and we never had any problems with him here.”

Documents show that Paddock and his wife, Peggy, divorced in 1990 for “irreconcilable differences,” and the couple does not appear to have had any children.

Paddock’s only real passion appears to have been gambling. Waitresses at a bar in Mesquite remember him as a regular customer who spent his afternoons playing video poker while drinking shots of tequila.

His brother Eric Paddock said Stephen Paddock was a multimillionaire and recently won a $40,000 jackpot.

“He was a wealthy guy who lived to play video poker,” Eric Paddock said. “He could do anything he wanted. He played multi-hundred-dollar-hand video poker.”

Six years ago, Paddock sued a different casino, the Cosmopolitan Las Vegas, alleging that while a guest at the hotel in 2011, he slipped on an unknown liquid on the casino floor, tearing a hamstring and spraining his wrist and hand. Surveillance video obtained by ABC News shows Paddock falling on the floor, then later being escorted to a back hallway of the casino where he is seen rubbing his leg and teetering in front of paramedics before being placed on a gurney.

Paddock said he had incurred over $32,000 in medical bills, but an arbitrator found the hotel had not been responsible and the case was dismissed in 2014. In his report, the arbitrator said evidence showed Paddock had been “en route to the high limit gambling area when he fell.”

While the suspect wasn’t familiar to authorities, his name should be. Eric Paddock told ABC’s Tampa, Florida, affiliate, WFTS, that their estranged father, Benjamin Hoskins Paddock, was a notorious bank robber who spent several years on the FBI’s Ten Most Wanted Fugitives list.

A wanted poster circulated in 1969 after his escape from a federal prison facility in Texas described the elder Paddock as a “very dangerous” criminal.

“Diagnosed as psychopathic,” the description reads. “Has carried firearms in commission of bank robberies. He reportedly has suicidal tendencies and should be considered armed and very dangerous.”

ABC News’ Rhonda Schwartz, Pierre Thomas, Gerry Wagschal, Cindy Galli, Jack Date, Pete Madden, Randy Kreider, Emily Shapiro, Alex Stone, Katie Conway, Erin Dooley and Kenneth Moton contributed to this report.