Your premise is bollocks. Untrue! I know, I've bouhgt guns. In Illinois, for instance, you cannot simply walk into a WalMart and buy ammunition without a STATE-ISSUED Firearms Owners ID card, which involves a background check. Indeed, to buy a weapon, you need either a Federal Firearms Licence OR to submit paperwork for the state background check and a waiting period. I know, I've done it, I have weapons, I have licenses!
The BIG DEAL here is why did he do it and how did he get the weapon we can hear on the videos? That sounds like an AUTOMATIC LONG GUN, which is illegal and only issued to military personnel. He was a 64 year old man living in a Retirement Community (have to be over at least 50 to live there) in Nevada, but also had property in N. Nevada, which is the Wild Wild West in terms of being out in the boonies and what people do up there. It is in the middle of nowhere and he may have had a range and cache of weapons up there and no-one would have known, or probably cared.
That said, none of this stops the next one, and the next, and the one after that....which will get us to the weekend! As others have noted, mass killings (4 or more) are a regular occurrence here, but until and unless the Second Amendment is repealed and the literally HUNDREDS OF MILLIONS OF FIREARMS removed from law-abiding people, there will always be ways to access guns. With a Republican President, Republican Senate, Republican House, and 3/4 of the State Houses in America run by Republicans, you can forget ANY LEGAL TIGHTENING....ANY...on the ownership of weapons in this country.
That is the reality of Firearms ownership in America, like it or not!