GUN CONTROL LAWS
The US has the most lenient firearm ownership laws. People can purchase weapons in the US from grocery or department stores. Unlike most other countries no permit is required and weapons can be purchased from a Walmart or from any local department store. The only pre-requisite is that you have no felonies or are not deemed mentally unstable.
WEAPONS SOLD ON THE MARKET
The United States does limit weapon sales of certain weapons namely defined as assault weapons. But a significant portion of the guns on sale are also categorized and legally sold as assault rifles. These with minor modifications or attachments, openly available in the market, can become more lethal then the weapons listed in the assault weapons category.
HOW DOES THIS TIE IN TO THE VEGAS SHOOTING?
I'd rather that you read this portion of this article then hear it from me.
"The Bureau of Alcohol, Tobacco, Firearms and Explosives disclosed that Paddock had outfitted 12 of his rifles with a legal device called a bump-fire stock, which enables a shooter to fire bullets rapidly, similar to an automatic rifle."
While automatic weapons are banned in the US accessories such as the Bump stock allow lethal assault rifles to essentially attain the same abilities. They can be purchased legally in the US. The Las Vegas shooter Stephen Paddock used these on all twelve of the weapons he was carrying.