The world was shocked on Sunday when 64-year-old Stephen Paddock opened fired on the Route 91 Harvest country music festival. Considered the worst and deadliest mass shooting in the United States, the Las Vegas shooting incident left at least 58 concertgoers dead and more than 500 people injured.

According to the authorities, Paddock started his deadly shooting spree from the 32nd floor of the Mandalay Bay Resort and Casino, where he had been staying since Sept. 28. At least 23 firearms, a sledgehammer, and 13 suitcases were found in Paddock’s hotel suite.

The Gunman

Stephen Paddock was the son of notorious bank robber Benjamin Hoskins Paddock, who was also registered on the Federal Bureau of Investigation’s (FBI) most wanted list for eight years after becoming a fugitive in 1969. He grew up in Sun Valley, California and attended California State University in Northridge.

For many years, Stephen was an accountant with a gambling habit but became a multimillionaire for his real estate investments, CBS News reported. Stephen had three brothers — Eric, Bruce, and Patrick — had been married twice but had no kids.

The Las Vegas shooting gunman lived in a home located at a retirement community in Mesquite, Nevada. He lived with his 62-year-old girlfriend, Marilou Danley, who was reportedly in the Philippines visiting her family at the time of the shooting.

In his Mesquite home, the police found more weapons including 19 firearms, explosives, electronics and thousands of rounds of ammunition.

The authorities also searched Paddock’s two-bedroom home in a Reno retirement community.

According to Stephen’s brother, Eric Paddock, the gunman had a couple of handguns that were all legal and one long gun that was kept in a safe. Eric also stressed that his brother was a "good guy" that had no “religious or political affiliations.”

Eric also believed that there's something that pushed his brother to do such violence.

Meanwhile, the authorities confirmed that Stephen wasn’t connected to any international terrorist group, despite the ISIS claiming responsibility.

The motive

Even though the motive is still under investigation, a law enforcement source revealed that Stephen had meticulously planned the attack. He also planned an earlier concert attack at the “Life is Beautiful” festival in Las Vegas last month.

The insider said that Stephen has tried booking rooms that were “strategically located to the festival” to carry out an attack. Unfortunately, the specific rooms he requested were already occupied.

Stephen also had outfitted his twelve rifles found in his hotel suite with a device called “bump stock,” which allows the shooter to fire hundreds of rounds per minute, as per The New York Times.

BBC News added that the police also found ammonium nitrate, a chemical compound that can be used in making explosives, in the gunman’s car.

Since Stephen’s quiet life didn’t sound off alarms, the authorities are having a hard time in identifying the motive behind the recent Las Vegas shooting. Stephen was also far from being a typical mass gunman as his age suggested that he’s almost 30 years older than most of the shooters.

Binghamton University professor, a forensic nurse and criminologist Mary Muscari also pointed out that Stephen’s method was “unusual.” Muscari explained that most of the shooters want a “face-to-face” encounter with their victims but Stephen carried out the shooting like a “sniper attack,” according to NBC News.

Marilou Danley

The authorities are hoping for the cooperation of Stephen’s girlfriend, Marilou Danley, "an Australian citizen originally from the Philippines and who plays a crucial part in the investigation. Experts said Danley can shed some insights into Stephen’s motivation and mindset.

Danley’s identification was also found on Stephen so she was initially considered a person of interest. But the police believed that she wasn't involved in Sunday's shooting incident after they contacted her.

On Tuesday night, Danley was met by the authorities upon her arrival at the Los Angeles International Airport. Meanwhile, The authorities also traced a recent money transfer of $100,000 into a bank account in the Philippines but the recipient has yet to be identified.