LAS VEGAS — A gunman at a Las Vegas hotel rained a rapid-fire barrage on a huge outdoor concert festival on Sunday night, sending thousands of people fleeing. At least 50 victims died, and hundreds of others were wounded, officials said, making it one of the deadliest mass shootings in United States history.

“We believe the individual killed himself,” said Sheriff Joseph Lombardo of the Las Vegas Metropolitan Police Department on CNN.

Online video of the attack outside the Mandalay Bay Resort and Casino showed the singer Jason Aldean performing outside at the Route 91 Harvest Festival, a three-day country music event, interrupted by the sound of automatic gunfire. The music stopped, and concertgoers ducked for cover. “Get down,” one shouted. “Stay down,” screamed another.
Several SWAT teams were sent to the hotel immediately after the first reports of the shooting at 10:08 p.m., and officers overheard on police radio reported being pinned down by gunfire. Shortly before midnight the Las Vegas police reported that “one suspect is down,” and soon thereafter the police said they did not believe there were any more active gunmen.

The Las Vegas police said Monday that 50 people were killed and 406 people had been taken to the hospital. The police identified the gunman as Stephen Paddock, 64. Sheriff Lombardo said the police were seeking “a companion” named Marilou Danley, and the authorities later said they were “confident” they had located her.

Eric Paddock, a brother of Stephen Paddock who lives in Orlando, Fla., told the Orlando Sentinel that he had made a statement to the police. “We are completely dumbfounded,” he said. “We can’t understand what happened.”
Video of the shooting captured nine seconds of rapid-fire, continuous bursts, followed by 37 seconds of silence from the weapon amid panicked screaming. The barrage of gunfire then erupted again in at least two more rounds, both shorter than the first.