Before any information had been released about the shooter's identity, or where and how he acquired the arsenal of 42 guns, 23 of which were eventually discovered in his hotel room, one Connecticut senator was already making headlines by exhorting Congress to "get off its ass" and pass gun-control legislation, officially marking the beginning of another contentious chapter in America's perennial gun-control debate.

"This must stop," Murphy said. "It is positively infuriating that my colleagues in Congress are so afraid of the gun industry that they pretend there aren't public policy responses to this epidemic."

He added: "The thoughts and prayers of politicians are cruelly hollow if they are paired with continued legislative indifference. It's time for Congress to get off its ass and do something."

Shortly afterward, the White House warned lawmakers not to turn the shooting into a "political debate" about gun control before all the facts have been determined. This turned out to be a prescient, because, as the public would later learn, it appears that Steve Paddock, the shooter, purchased his guns legally.

Paddock, who was described by his brother as a millionaire real-estate investor, had no criminal history nor any history of mental illness. Before purchasing guns from two licensed dealers earlier this year, Paddock passed federally mandated background checks. In an interview with NBC, the owner of a gun dealer where Paddock purchased weapons earlier this year said ATF agents had interviewed the employee who made the sale, and confirmed that the dealer had followed all legally necessary procedures before completing the sales.

David Familglietti of New Frontier said that Paddock purchased a rifle and a shotgun in the spring and that agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives interviewed the employee who handled the sale.

"The rifle was not fully automatic, and a shotgun isn't capable of shooting from where he was," Famiglietti told NBC News when asked whether it was possible that the guns were used in the mass shooting.

"He's only shopped there once, so it wasn't someone we knew personally," he said.

"We're very sad about the news of this tragedy. We're in the business of selling firearms legally and took all precautions on this sale, as we do with all sales. My staff takes their job very seriously, and if there were any 'red flags,' the sale would have halted immediately."