STEVE INSKEEP, HOST:
And I'm Steve Inskeep in Las Vegas. The sheriff here has been calling Sunday's mass shooting premeditated, and this morning we have a better idea just how premeditated it was. The gunman modified many of his rifles to fire somewhat like automatic weapons. He also, we now know, set up cameras to watch his back. And that's where we begin with NPR's Martin Kaste, who's been following the investigation. He's here in Las Vegas with us. Hi, Martin.
MARTIN KASTE, BYLINE: Good morning.
INSKEEP: So how did he position the cameras?
KASTE: Well, it looks like he had sort of a defensive perimeter at the entrance to his room. He was at the end of the hallway. He had two cameras out in the hallway looking down the hall, another camera in the peephole of the door. And police believe it was a way for him to keep an eye on who was coming up behind him as he was doing his deed. And we know that a security guard for the hotel was shot through the door early into the assault. So it looked like he was keeping an eye out who was coming up.
INSKEEP: And ever since we heard the video of those long bursts of what seemed like automatic weapons-fire, we've been wondering how he modified his guns.
KASTE: Yeah, and it looks like we now have confirmation that he was using what are called bump fire stocks. Twelve rifles had these attachments on them. And now, as you know, a semi-automatic rifle, which is legal in this country, is the kind of rifle where you - for every round, you have to pull the trigger.
INSKEEP: One shot for each pull, yeah.
KASTE: Every time, you pull the trigger. A fully-automatic rifle, which is illegal, to sell at least a new one, is a steady stream - one pull, one trigger pull. These bump fire stocks let you convert from the pull-per-bullet to something where you get a steady stream.
INSKEEP: Meaning it fires like an automatic weapon, but, is it legal?
KASTE: This used to be a gray area. But a few years ago, the government decided that these are indeed legal, technically legal. This is how Jill Snyder of the ATF, who's on this case, explained this.
JILL SNYDER: The classification of these devices depends on whether they mechanically alter the function of the firearm to fire fully automatic. Bump fire stocks, while simulating automatic fire, do not actually alter the firearm to fire automatically, making them legal under current federal law.
INSKEEP: Simulating automatic fire?
KASTE: Yeah. I mean, if you're on the receiving end, it probably doesn't seem like a simulation, but this is legal because it obeys the letter of the law in that it doesn't modify the mechanism internally to the gun. You're not making - you're not making changes inside. Instead this adapter sort of takes advantage of the recoil energy when you fire the first bullet and keeps using that energy to sort of shove your finger against the trigger for you, and so you get a steady stream.
INSKEEP: Although we're also learning in recent days, and gun owners will know this, it's not manufactured - the gun is not manufactured to fire so many bullets so quickly, and it overheats.
KASTE: No. And in fact it jumps around a lot, too, when you fire it this way, so you lose accuracy. And the overheating of this gun firing at that rate means it'll jam up fast, which probably accounts for why he had 12 of these so he could swap guns as they heated up.
INSKEEP: Is there any more insight into why the gunman acted this way?
KASTE: Not really yet on why he was thinking what he was thinking. We don't know that. But there is a lot of interest right now on the person who's being characterized as his girlfriend, Marilou Danley. Police say he's - she's been out of the country since before the attack. Last night she came back. She flew to Los Angeles. She was met there by law enforcement officials, and she's expected to be questioned. They've been calling her a person of interest. That means she's not necessarily a suspect here, but I think they hope that she can shed some light on what led up to this, especially because there have been some reports now that the shooter sent money overseas to the Philippines, where she was.
INSKEEP: So Martin, he's sending money to the Philippines. He's stockpiling weapons. He's modifying weapons. He's bringing in cameras. Is this level of preparation normal for people committing these kinds of mass killings?
KASTE: Normal? Well, it is not unprecedented. In mass-shooter situations, there's often a pattern here of preparation, of setting yourself up, of thinking through what you're going to do, amassing an arsenal. So I'm afraid this doesn't look that strange.
INSKEEP: Martin, thanks very much.
INSKEEP: That's NPR law enforcement correspondent Martin Kaste this morning. Transcript provided by NPR, Copyright NPR.