Some states have long allowed its citizens to own full auto weapons. Go to Gunbroker and then go to "Class 3" then go to machine guns.
Nevada happens to be one of those states that allows its citizens to own full auto. As an aside, there are numerous states that do so, and there are lots of full autos in private ownership. I'll be very, very surprised if this shooter was using a legally acquired full auto weapon.
I had no idea fully automatic rifles are legal ANYWHERE. I’ve always heard about it being illegal to convert a rifle to fully automatic.
This guy definitely had the bucks. He owned two airplanes.