According to BBC, the gunman, Stephen Paddock, opened fire from the 32nd floor of the Mandalay Bay Hotel towards an open-air music festival on Sunday evening.
The final shows of the three-day Route 91 country music festival were in full swing when the gunman struck.
According to police, Paddock had booked into the hotel four days earlier, on 28 September.
Police found 23 guns in the 64 year olds hotel room, as well as "in excess of" 19 firearms and explosives at his Nevada home.
But as yet, no clear reason for the killing has emerged.
Investigators have found no link to international terrorism, despite a claim from so-called Islamic State. Some investigators have suggested psychological issues, but there is no confirmation of this. BBC reports.
The shooter was not known to police.
President Donald Trump described the attack as "pure evil" in an address from the White House on Monday.