We may have an answer to the question I asked this morning. The Wall Street Journal reported hours ago that cops found 18-20 guns in Paddock’s hotel suite at Mandalay Bay, “some fully automatic.” That seems hard to believe, though. Automatic weapons are exceptionally difficult to come by and are almost never used by criminals. Said one gun expert to NBC, “Most big city police departments, if you asked them the last time they had a crime where a fully automatic weapon was used, most will say they don’t know of any.” If Paddock had even one, it would be surprising. Multiple would be amazing.

But what if, by “fully automatic,” the Journal’s sources meant semiautomatic weapons that had been modified with accessories to mimic fully automatic guns, firing at a similar rate? That’s far more plausible. Per the AP, there’s reason to believe that’s what happened:

Two officials familiar with the investigation say authorities found at least 17 guns in the hotel room of the Las Vegas shooter.

Stephen Paddock also had two devices that are attached to the stocks of semiautomatic guns to allow fully automatic gunfire. The bump-stock devices have attracted scrutiny in recent years from authorities.

A human can’t simulate automatic fire on a semiautomatic naturally because a finger can’t pull the trigger fast enough. A “bump stock” ingeniously avoids that problem by making the gun itself do the work. The Trace describes how it operates: “Instead of pulling back the trigger to fire, the user places his or her finger slightly in front of the trigger and pushes the whole gun forward with steady pressure. The trigger hits the finger and the round goes off. Recoil pushes the gun back, but the shooter’s forward pressure immediately returns the trigger back to the finger, and so the gun fires off another round faster than the blink of an eye.” If you want to see what it looks like in practice, behold:

Indistinguishable from automatic fire to the layman’s eye, so much so that you wonder why Paddock would have gone to the trouble of obtaining a fully automatic weapon if he could mimic one this closely with a cheap, legal modification. Although maybe not legal for much longer: It’s a cinch Democrats will come after bump stocks now, especially if it turns out that they were what Paddock used to generate his rate of fire rather than a conventional automatic. The NRA and the GOP will have a tough time playing defense on that. The argument for banning the stocks will be that they allow mass killers to fire many more shots in a given amount of time than a conventional semiautomatic can, making them potentially much more lethal before the police arrive. The argument against banning bump stocks is … they’re cool at the range? It’s an affront to the Second Amendment to ban de facto machine guns … even though actual machine guns have been banned for ages? Who knows if Trump will even go along with the party on this?

Two of the gun shops from which Paddock bought weapons say they didn’t sell him anything unusual and he passed all background checks. As far as I’m aware, he had no criminal record — and yet, not only did he have an arsenal in his hotel suite, he also reportedly had ammonium nitrate in his car, the same explosive used by Timothy McVeigh in the Oklahoma City bombing. This is a strange, strange case.