In the days before the attack, he was holed up in a suite at the Mandalay Bay hotel, located on The Strip.
"It was pre-planned, extensively, and I'm pretty sure that he evaluated everything that he did in his actions, which is troublesome", Joseph Lombardo, the sheriff of the Las Vegas Metropolitan Police Department, said. The shooting went off and on for nine to 11 minutes, he said.
Snyder said 12 of the guns found in the hotel room were fitted with so-called bump-stock devices that allow the guns to be fired virtually as automatic weapons.
Jill Snyder, the special agent in charge at the Bureau of Alcohol, Tobacco and Firearms, tells "CBS This Morning" on Wednesday that Paddock purchased 33 firearms, mostly rifles, between October 2016 and September 28, three days before he opened fire on a concert crowd.
Authorities said Paddock, who had no criminal record, smashed windows in his hotel room shortly after 10pm on Sunday and rained fire on a crowd of some 22,000 attending a country music concert below.
"The genetics load the gun, personality and psychology aim it, and experiences pull the trigger, typically", Clemente said.
Authorities have been at a loss as to how a 64-year-old gambler and retired accountant had hauled a vast arsenal of weapons to the hotel and launched his assault.
Danley, an Australian citizen reported to have been born in the Philippines, has not been charged in the case and told her family she has a "clean conscience" following the Las Vegas attack, her brother said in an interview with ABC News in the Philippines. The couple lived in a retirement community in Mesquite, Nevada, which is outside of Las Vegas.
In one Facebook post, Danley describes her daughter and her granddaughter, who is a fourth grader, as "my 2 precious jewels and love of my life!".
The investigation of a gunman who killed 59 people at a Las Vegas concert now shifts to his girlfriend, who has returned to the United States from the Philippines.
In the days before the shooting, Mr Paddock transferred $US100,000 ($A127,700) to the Philippines, a United States official briefed by law enforcement told the Associated Press on the condition of anonymity.
Law enforcement officials who confirmed the wire transfer to NBC did not reveal who the bank account belongs to. The FBI is working with Filipino authorities to determine details.
Authorities are investigating reports that while she was in the Philippines, Paddock wired her $100,000.
The sisters, who were not identified by name and whose faces were blurred, added that Danley would willingly cooperate with investigators.
A flight attendant from the plane declined to comment, as did an airline manager at the terminal, citing privacy concerns, when asked if they had seen Danley. Stanton said Lombard is expected to put out a statement later Wednesday.