Investigators said Paddock had no known connection to international terrorism, and there were no other shooters. Nonetheless, ISIS claimed responsibility and offered no evidence.
"We have determined to this point no connection with an international terrorist group," the FBI said. "We will continue to work with our partners to ensure that this is factually, thoroughly and absolutely investigated to be able to bring comfort and peace back to this community."
Police told The Wall Street Journal that the shooter appears to have used a fully automatic rifle. Law enforcement authorities discovered a cache of at least 18 other firearms in the shooter's hotel room where he fired upon those below. Another 18 firearms were retrieved from the suspect's house, authorities said late Monday.
Videos posted on social media showed large crowds ducking for cover amid sustained blasts of gunfire.
The FBI requested that anyone with video or photos regarding the shooting call 1-800-225-5324.
Lombardo said a woman who was a "companion" of Paddock, Marilou Danley, has been located, as were two vehicles associated with the shooter: a Hyundai Tucson and a Chrysler Pacifica, both with Nevada number plates. Police say Danley was not with Paddock when he checked into Mandalay Bay. Paddock was utilizing some of her identification, Lombardo said, adding that police "have had a conversation with her," and that she was not believed to have been involved "at this time."
During the shooting, police told people to avoid heading to the south end of the Strip and said it was investigating an active shooter. Police said Las Vegas Boulevard was shut down southbound at the Tropicana.
The number of dead surpassed the death toll in the June 12, 2016, rampage at the Pulse gay nightclub in Orlando, where 49 people were slain. Police said among the injured were two on-duty officers. One was in stable condition after surgery and the other sustained minor injuries.
Lombardo also said reports on social media that there were multiple shooters and explosives used were false.