It was staged for two days and drew more than 65,000 people.
TMZ reported that Paddock specifically asked for rooms with a view of Grant Park.
Earlier this week, the Daily Beast reported that Paddock might have targeted another Las Vegas festival, Life Is Beautiful, the weekend before, and had rented out rooms at the Ogden, a hotel about eight miles away from Mandalay Bay. The Chicago Sun-Times quoted a source at the hotel who confirmed the booking.
Investigators believe Paddock used a device similar to a hammer to smash two windows in his room before he opened fire on the music festival crowd, shortly after a rendition of "God Bless America".
Paddock checked into his room at the Mandalay Bay Hotel on September 28, three days before carrying out his deadly attack, Clark County Sheriff Joseph Lombardo said.
"You've got to make the assumption he had to have some help at some point".
Lombardo said Paddock's auto had 50 pounds of explosives, and 1,600 rounds of ammo.
Lollapalooza is a yearly concert festival that takes place in Chicago.
A former executive casino host at the Atlantis Casino Resort and Spa in Reno, Nevada, where Las Vegas shooter Stephen Paddock frequently gambled, says Paddock had a "god complex" and expected quick service no matter how busy employees were. Lombardo said at a news conference.
As it turned out, Paddock never showed.
2pm: Sheriff says Marilou Danley is a person of interest again, after report that Paddock wired $100,000 to an account in the Philippines a week before the attack, while she was in the country.
An executive casino host described Las Vegas shooter Stephen Paddock as an analytical gambler who would try to identify video poker machines most likely to provide big pay-offs.
Danley spent much of the day being questioned by Federal Bureau of Investigation agents in Los Angeles, where she arrived from the Philippines. She said she had no inkling of his murderous plans.
"It never occurred to me in any way whatsoever that he was planning violence against anyone".
Mr. Moulton said the ban has to be passed by law and not through a regulation from the Alcohol, Tobacco and Firearms Bureau because that agency works within the laws as they're written.