How could someone obtain or buy such a weapon?
Easily, in many states, including Nevada and Arizona.
But without all the facts about the guns used by mass murderer Stephen C. Paddock, his exact route to fully auto remains unknown as of Monday morning.
Paddock, shooting from the 32nd floor of the Mandalay Bay hotel, killed at least 58 people and wounded hundreds more in the Sunday-night attack on concertgoers at the Route 91 Harvest Festival before reportedly killing himself.
From the audio released of the shooting, "it's something I would characterize as being a machine gun," said Alcohol, Tobacco, Firearms and Explosives bureau spokesman Thomas Mangan, adding that he didn't yet have information about the type of guns used.
Considering the long duration of the shots fired, "obviously we'd be looking at extended magazines, maybe a drum" to hold the ammunition. "One burst I heard was 12 seconds — he had a good amount of ammo up there."
Paddock had a stash of at least 17 guns, including 10 rifles, in the hotel room, according to media reports, but the type and configuration of each hasn't yet been revealed. (UPDATE: Unnamed sources later told the Washington Post that one rifle was an “AK-47 type” mounted on a stand, and that other weapons recovered ranged in caliber from .223 to .308. Spotting scopes and a handgun were also found among a total of 17 guns in the room.)
People can buy fully automatic rifles in gun stores: Mangan estimates an average of one per day is sold in Arizona. Buyers must obtain federal registration of the weapon for a fee, plus fingerprinting and a background check.
The Internet is furious that Las Vegas gunman Stephen Paddock isn’t being described as a terrorist https://t.co/1zrkdqEYUE— Raw Story (@RawStory) October 2, 2017
Buyers wouldn't normally be able to walk into the gun store to order a machine gun, then walk out the same day with one — the whole process takes 90 to 120 days. Only machine guns made before 1986 can be legally sold in the United States, and that has resulted in a finite population of 125,000 such guns, which usually cost between $18,000 and $40,000.
"It's an expensive hobby to be buying machine guns," Mangan said. "Just speculating, but it's not somebody really off the street that invests that much money into machine guns."
The cheaper method is to convert an off-the-shelf, semiautomatic rifle — for which registration isn't required — and convert it to shoot full-auto.
"There is a black market — a dark web on that," he said.
The conversion parts could have been obtained in or outside of the United States, he said. "If someone wants to get their hands on these materials, it's quite easy to do that."
Rick Vasquez, a retired ATF expert and former head of the agency's Firearms and Technology branch, said "there is no doubt in my mind it was an automatic weapon" in Sunday's massacre.
Converting a rifle to full-auto might be tough for some people, but simple for someone with the right technical know-how and proper tools, said Vasquez, who's also a U.S. Marine Corps veteran and runs a firearms-consulting business in Virginia. Often, it's done by drilling a hole in the legal weapon to allow it to accept a part called a drop-in sear, which converts a semiautomatic AR rifle into a machine gun.
Motorcycle outlaws and drug-dealers selling them to people who ship the parts or guns "south of the border" make up the majority of cases of illegal fully automatic gun sales, he said.
"The average guy doesn't do this because it's a 10-year felony offense," Vasquez said. While someone with a clean record who possesses an drop-in sear or rifle converted to full auto might not get 10 years for a first offense, a prohibited possessor — someone who's had his or her gun rights taken away — "is going to jail for a long time."
The stiff penalties are the likely reason converted guns aren't more widespread, or used in more mass-shootings, he said.
For people who illegally own such a weapon, it's difficult to shoot it without someone noticing, he pointed out, adding that most gun-range personnel would ask to see the paperwork on a machine gun being fired at their facility.
The way the festival crowd was "corralled" behind gates, "it was a mass-murderer's dream," he said. "The best safety is just being aware of the situation. But in a situation like this, what is your awareness going to do?"
Vasquez said he worries about copycat killers.
Arizona gun guru Alan Korwin, an author of books on gun laws, also expressed concern about copycats. In his view, repeatedly showing a mass murderer's photograph, whether it's someone like Paddock or Osama bin Laden, "the media inspires evil gleefully ... it's way beyond any newsworthy value."
News reporters affect their consumers psychologically by calling the murderer a "shooter," and they "promote" news of such massacres, rather than just reporting the facts, Korwin said.
Displaying the murderer's photo "ad nauseam" could conceivably "encourage some other maniac," he said.
Meanwhile, gun-control groups ramped up their messaging on Monday in the wake of the massacre.
“I know this feeling of heartbreak and horror too well," former Congresswoman Gabrielle Giffords said in a written statement sent to the media.
Giffords was shot in the head and wounded severely during the January 8, 2011, massacre in a Tucson parking lot that claimed six lives. She's the co-founder of Americans for Responsible Solutions. "The massacre in Las Vegas is a grave tragedy for our nation. This must stop — we must stop this. ... Now is the time to take positive action to keep America safer. Do not wait. The nation is counting on you.”
Hillary Clinton used the massacre to criticize the Hearing Protection Act, a Congressional bill that some say would make it easier for the public to buy silencers.
"We can and must put politics aside, stand up to the NRA, and work together to try to stop this from happening again," she tweeted on Monday.
The National Rifle Association did not release a statement on the Vegas tragedy as of Monday morning.