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Police spoke of how Stephen Paddock carefully planned his actions before he opened fire on concertgoers at a "progressively rapid rate" through windows on the 32nd floor of the Mandalay Bay Hotel and Casino.
He placed one camera in a food service cart in the corridor, while a second camera was placed outside his room and a third in the peep hole of his two-room suite, officials said.
Details of the 64-year-old's meticulous planning emerged as Paddock's girlfriend, Philippines-born Marilou Danley, arrived back in the US on Wednesday for questioning.
Investigators are examining a $100,000 wire transfer the killer sent to an account in the Philippines that "appears to have been intended" for Ms Danley.
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Ms Danley is said to have shared Paddock's apartment block at a retirement community in Mesquite, Nevada, about 90 miles (145km) northeast of Las Vegas, where police found 19 more guns after discovering 23 in his hotel room.
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Five handguns, two shotguns and a "plethora" of ammunition were discovered at another property Paddock owned in Reno, Nevada.
Investigators who searched his hotel room also found a computer and 12 "bump stock" devices , which enable a rifle to fire continuously, like an automatic weapon.
Police said the shooting continued for 11 minutes, between 10.08pm and 10.19pm on Sunday.
Paddock used at least 10 suitcases to smuggle the weapons into his room after checking in on Thursday last week.
Images posted by US media showed automatic weapons attached to tripods lying on the ground of the hotel room, with scores of bullet casings littering the floor around them.
At a news conference, Clark County Sheriff Joe Lombardo said: "The fact that he had the type of weaponry and amount of weaponry in that room, it was pre-planned extensively."
"Bump stock" devices are legal under US law, even though fully automatic weapons are for the most part banned.
During his killing spree, Paddock shot a security guard who approached the room in the leg.
Patrol officers acting on their own and without the direction of a supervisor were the first to react to the situation and close in on Paddock's room.
The officers evacuated people from the 29th to 32nd floors before converging on the attacker's suite.
A SWAT team then used explosives to gain entry, where Paddock's body was found among his arsenal of weapons.
The millionaire retired accountant, who liked to gamble and invest in property, killed himself, police believe.
All but three of those who died have now been identified. More than 500 others were injured in the attack.