Stephen Paddock, the man who went on a killing rampage in Las Vegas on Sunday night (Oct. 1), meticulously planned his crime in advance for maximum death and destruction, investigators have revealed.

The 64-year-old retired accountant killed at least 58 people and wounded more than 500 more during a mass shooting that authorities are now saying lasted as long as 11 minutes on Sunday night, during which he fired down into the crowd at the Route 91 Harvest Festival from his hotel room, beginning during Jason Aldean's headlining set.

Clark County Sheriff Joe Lombardo says that Paddock used video cameras to watch for police to storm his hotel room on the 32nd floor of the Mandalay Bay Resort and Casino as he continued his killing spree.

“It was preplanned, extensively, and I’m pretty sure that he evaluated everything that he did in his actions, which is troublesome,” Lombardo said, according to the Washington Post.

Paddock hid one camera in the peephole of his room and two more in the hall, investigators say. One of the cameras was disguised on a service cart, and at one point during Paddock's shooting spree, his pre-planning allowed him to shoot through the door of his room and wound a security guard who was approaching from outside.

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Paddock later put a gun in his own mouth and fatally shot himself as SWAT officers closed in. Authorities have yet to determine any motive for Paddock's crime, which is the worst mass shooting in modern U.S. history. He does not fit any mass shooter profiles, though Lombardo said Tuesday that they are "making progress" in that area.

So far the investigation has revealed a picture of an anti-social loner who may have been worth as much as $2 million and who frequently indulged in a passion for high stakes gambling. Paddock had not been in trouble with the law prior to his attacks, but one possible clue may lie in his father, a bank robber who was once on the FBI’s most-wanted list and who authorities described as a “psychopath."

The Post reports that on July 28, 1960, when Paddock was 7, a neighbor took him swimming because she knew authorities were coming for his father, and she wanted the boy to avoid the trauma of watching his father being taken away. That incident reportedly deeply affected Paddock's family, though his brother notes that their father was not in their lives as children. Neighbors have described Paddock as "surly, unfriendly and standoffish," the Post reports.

On Tuesday night, Paddock's girlfriend, 62-year-old Marilou Danley, returned to the U.S. from the Philippines, where her sisters say Paddock had surprised her with a ticket and encouraged her to get out of town. Initially described as a person of interest, she is facing questions in order to help establish a possible motive, though her sisters insisted in an interview with CNN's Australian affiliate that she knew nothing of what Paddock was planning.

“I know that she don’t know anything [about the attacks] as well like us,” Danley’s sister states. “She was sent away. She was away so that she will be not there to interfere with what he’s planning.”

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