A federal law enforcement official earlier said two rifles were outfitted with scopes and set up on tripods in front of two big windows. Another official said that among the weapons were AR-15-style assault rifles. Both officials spoke on the condition of anonymity because they were not authorized to divulge details of the investigation.

Sheriff Lombardo said that Mr. Paddock brought at least 10 suitcases into his hotel room over a period of time.

The sheriff said that Mr. Paddock fired through his hotel room door at security guards, striking one in the leg. The guard is still alive, he said. SWAT officers went in after the guard was shot.

In addition to the weapons at the hotel, the sheriff said the police retrieved 19 firearms, as well as explosives, several thousand rounds of ammunition and “electronic devices” from Mr. Paddock’s home in Mesquite, Nev.

Paddock raised no suspicions at a store where he bought firearms.

The investigation into Mr. Paddock’s gun arsenal led investigators to New Frontier Armory, a large North Las Vegas dealer, distributor and manufacturer of firearms.

David M. Famiglietti, the company’s president, issued a statement on Tuesday confirming that Mr. Paddock purchased “several” rifles and shotguns from the business last spring — all at the same time. It’s not uncommon for customers to do this to save money on background check fees, Mr. Famiglietti said.

“The firearms he purchased did not leave our store capable of what we’ve seen and heard in the video without modification,” he said. “They were not fully automatic firearms, nor were they modified in any way — legally or illegally — when they were purchased from us.”

Mr. Famiglietti said that nothing about Mr. Paddock raised red flags with the store’s sales clerk. On the contrary, according to Mr. Famiglietti, Mr. Paddock seemed to be interested in competitive shooting, asking the clerk a lot of questions about three-gun shooting matches — an increasingly popular sport in which players use a rifle, a shotgun and a pistol.

“He just seemed like a normal guy,” said Mr. Famiglietti, whose store has been the target of hate mail, threatening phone calls and fake reviews since the shooting. “We obviously did not sell him these firearms with the intent that he would use them to hurt anyone in any way.”

On Monday, a Mesquite, Nev., gun dealer, Guns & Guitars, acknowledged having sold two rifles and a handgun to Mr. Paddock. Like the purchases at Frontier, those were cleared by state and federal background checks.

The gunman was ‘not an avid gun guy at all,’ said one of his brothers.

Mr. Paddock, 64, was described as a high-flying gambler who lived in a quiet retirement community and played golf. Officials said he had no significant criminal history and drew little attention to himself.

Investigators are trying to piece together his financial history to search for clues that could help determine what set him off.

Image Stephen Paddock in a photo provided by his brother Eric Paddock. Credit... via Associated Press

Mr. Paddock often bet heavily at the major casino hotels, and his girlfriend, Ms. Danley, 62, who was out of the country at the time of the shooting, had worked for some of those hotels. They lived in Mesquite, Nev., 80 miles northeast of Las Vegas, and he also owned a home in Reno.

Ms. Danley boarded a flight from Manila to Los Angeles on Tuesday, according to Antonette Mangrobang, a spokeswoman for the Philippine Immigration Bureau. The authorities, who met Ms. Danley at the Los Angeles airport, have called her a “person of interest” in the shooting investigation, which does not necessarily mean that she is suspected of committing a crime.

‘I’ve never been that scared in my life,’ said one witness.

The police estimated that when the shooting began, there were 22,000 people at the Harvest Festival, listening to Jason Aldean, the final act of the three-day event.

Video of the shooting captured nine seconds of continuous, rapid fire, followed by 37 seconds of silence from the weapon and panicked screaming from the crowd. Gunfire then erupted again and again in extended bursts. Some concertgoers thought the noise was fireworks, but as it became clear what was happening, people fled, many of them unsure where the shots were coming from, or where they should go.

“Everyone was running, you could see people getting shot,” said Gail Davis, one of the witnesses. “I’ve never been that scared in my life,” she added. “To have this happen, I can’t wrap my mind around it.”

Video from the shooting showed Mr. Aldean running off the stage as the gunfire erupted.