The death toll, which officials said could rise, surpassed last year's record massacre of 49 people at a gay nightclub in Orlando, Florida, by a gunman who pledged allegiance to Islamic State.
Paddock, however, seemed atypical of the overtly troubled, angry young men who experts said have come to embody the profile of most mass shooters.
Public records point to an itinerant existence across the U.S. West and Southeast, including stints as an apartment manager and aerospace industry worker. But Paddock appeared to be settling in to a quiet life when he bought a home in a Nevada retirement community a few years ago, about an hour's drive from Las Vegas and the casinos he enjoyed.
His brother, Eric, described Stephen Paddock as financially well-off and an avid enthusiast of video poker games and cruises.
"We're bewildered, and our condolences go out to the victims," Eric Paddock said in a telephone interview from Orlando, Florida. "We have no idea in the world."
Las Vegas's casinos, nightclubs and shopping draw more than 40 million visitors from around the world each year. The Strip was packed with visitors when the shooting started shortly after 10 p.m. local time on Sunday during the Route 91 Harvest music festival.
The gunfire erupted during the Route 91 Harvest music festival as country music star Jason Aldean was performing. The musician ran off stage as the shooting progressed.
Video of the attack showed throngs of people screaming in horror and cowering on the open ground as extended bursts of gunfire strafed the crowd from above, from a distance police estimated at more than 500 yards (460 meters).
The bloodshed ended after police swarming the hotel closed in on the gunman, who shot and wounded a hotel security officer through the door of his two-room suite and then killed himself before police entered, authorities said.
Police said 23 guns were found in Paddock's suite.
Lombardo said a search of the suspect's car turned up a supply of ammonium nitrate, a fertilizer compound that can be formed into explosives and was used in the 1995 Oklahoma City bombing of a federal office building that killed 168 people.
Police found another 19 firearms, some explosives and thousands of rounds of ammunition at Paddock's home in Mesquite, about 90 miles (145 km) northeast of Las Vegas.