It is not legal to purchase automatic weapons in Las Vegas or anywhere else in the United States. Automatic weapons are taxed extremely high and are vetted by ATF individually.

Nevada is not even in the "top ten" of laxest gun laws in the United States.

The suspect was also planning to build a fertilizer bomb. He had apparently started to build one. That would have been far more destructive.

Ultimately, insane people do insane things. We have laws on the books to try and stop them. Stricter laws do not equate to less gun violence. The opposite is actually true. Every mass shooting in the United States with few exceptions, have happened in "gun free" zones. Chicago, which DOES have the strictest gun laws, has more murders per year than some entire states.