Forty-seven firearms from three locations. Piles of ammunition, and devices that converted assault rifles to automatic weapons that fired like machine guns.

How did Las Vegas gunman Stephen Paddock, who shot and killed 58 people from his 32nd story hotel window, amass an arsenal of firearms? In the United States, and particularly in states like Nevada, it's easy. And totally legal.

Although the country is notorious for its lax gun laws, there are some restrictions on multiple sales of handguns. But if someone wants to build up a cache of rifles the way Paddock did, they could do so without anyone noticing.