At 10:08 p.m. on Sunday, the shooter opened fire on the thousands of people attending a country music festival a few hundred yards northeast of the hotel, firing long, rapid-fire bursts into the throng, as people screamed and ran for their lives. He killed 59 people — all but three have been identified, the sheriff said on Tuesday — and wounded hundreds of others. In all, more than 500 people were injured, most by gunfire, and some in the panicked rush to escape.
President Trump, who is expected to visit Las Vegas on Wednesday, said on Tuesday that Mr. Paddock was “a sick man, a demented man,” adding that “we are dealing with a very, very sick individual.” He said there would be some discussion about firearms legislation, but was not specific.
“We will be talking about gun laws as time goes by,” Mr. Trump said as he prepared to leave Washington for hurricane-battered Puerto Rico.
Sheriff Lombardo said that Mr. Paddock, 64, had set up cameras in the hotel, but he did not know if they were used to record the scene — which could provide crucial evidence — or merely for surveillance of his surroundings. The FBI took the equipment and is examining it.
“I anticipate he was looking for anybody coming to take him into custody,” the sheriff said. “There was cameras located outside of the room and inside of the room,” including one placed on a service cart in the hallway.
The gunman had 23 firearms, including military-style rifles, and hundreds of rounds of ammunition in Suite 32135, and the sheriff has said that Mr. Paddock had used more than one of the guns to fire on the crowd. Another law enforcement official, who was not authorized to discuss the matter publicly and spoke on condition of anonymity, has said that two of the weapons had been set up with tripods and scopes to aim through two windows the gunman had smashed.
Mr. Paddock checked in on Thursday, and kept the “Do Not Disturb” sign on his door for the next three days, so no maids entered the rooms, according to a housekeeping manager, who also was not authorized to discuss the matter. Housekeepers are allowed to enter a room with such a sign only in the presence of a security guard, and it happens rarely, usually after several days, the manager said.
The hotel staff is trained to look for anything suspicious, but the gunman’s behavior did not set off any alarms, the manager said. He had at least 10 suitcases in his room, the sheriff had said, which might have been used to bring the guns in without notice. But the manager said it would have been easy to bring them to the room a few at a time without arousing suspicion.
Semiautomatic rifles, like those the gunman had, are made to fire a single round with each pull of the trigger. But recordings and witness accounts of the shooting made clear that the shooter was firing much faster, at a rate comparable to that of a fully automatic weapon, which quickly fires round after round with a single pull of the finger.
But replacing the standard rifle stock, which rests against the user’s shoulder, with a bump stock like the one Mr. Paddock had, allows a semiautomatic rifle to fire much more rapidly, like an automatic, firing hundreds of rounds per minute — much faster than a person can pull and release the trigger. The devices are usually legal and inexpensive, with some versions advertised for $99.
A bump stock allows the body of the rifle to slide a short distance back and forth, harnessing the recoil energy of each shot. The weapon bounces, or “bumps,” rapidly between shoulder and finger, essentially creating the action of repeated trigger pulls without the shooter having to move the trigger finger.
Senator Dianne Feinstein of California, a Democrat, has called for years for a ban on bump stocks, and she renewed that call on Tuesday, writing on Facebook, “this is the least we should do.” Congressional Democrats asked their Republican counterparts to establish a special committee to investigate gun violence.
Senator Mitch McConnell, the Republican majority leader, rebuffed questions about potential legislative action during his regular news conference Tuesday afternoon, saying that the massacre was being politicized.
“Look, the investigation’s not even been completed,” Mr. McConnell said. “And I think’s it’s premature to be discussing legislative solutions, if there are any.”
Senator John Thune, the third-ranking Republican in the Senate, told an NBC News reporter that lawmakers “ought to take a look at” conversion kits that can make guns more lethal. But Mr. Thune also suggested little could be achieved through legislation.
Mr. Paddock was an avid gambler who often bet heavily at the major casino hotels, and his girlfriend, Marilou 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.
Police have found a total of 49 firearms in his two houses and his hotel suite. Several news organizations published photos that they said showed parts of the scene inside and just outside the hotel suite, including rifles on the floor, some of them on tripods, surrounded by spent ammunition shells.
“I can’t verify whether they’re legitimate or not,” Sheriff Lombardo said of the photos. “What I can tell you is I’m very troubled by it. We have an internal investigation occurring as we speak on how those photographs were obtained.”
Law enforcement officials have said they are confident that Mr. Paddock, who had no prior criminal record, was the sole shooter on Sunday. Though the Islamic State group has claimed that he was one of their followers, officials say that, so far, they have found no evidence that he had ties to any extremist group.
But Mr. Lombardo stressed that investigators were still looking into what roles others might have played. “I assure you this investigation is not ended with the demise of Mr. Paddock,” he said.
Asked if Ms. Danley was considered a suspect, he said, “currently she’s a person of interest.”
Mr. Paddock recently wired thousands of dollars to the Philippines, but it was not clear who the recipient was.
His work history was not entirely clear; his brother has described him as a wealthy retiree. Mr. Paddock worked for the federal government for roughly 10 years, from 1975 to 1985, a spokeswoman for the Office of Personnel Management confirmed Tuesday.
Investigators unearthed multiple job applications, with Mr. Paddock’s fingerprints on file, as part of records reflecting his employment as a letter carrier for the Postal Service in the mid-1970s; as an I.R.S. agent from 1978 to 1984; and as an auditor focused on defense contracts, a job he held until 1985. He also worked in the 1980s for one of the companies that later combined to form Lockheed Martin, the aerospace contractor.
Mr. Paddock’s and Ms. Danley’s neighbors in Reno described the couple as quiet and private, and Mr. Paddock as a recluse they rarely saw. Susan Page, a retired financial analyst who lives next door, said she never saw anyone visit them.
“It wasn’t that they were unfriendly, they just didn’t socialize,” she said. “I thought maybe he was sick or something because they were always in the house and the shades were always drawn shut.”