Wildly misinformed people.

First people here are confusing civilian semi-auto assualt type rifles with their miltary full-auto counter parts. In most states Semi-auto, civilian Assualt rifles are as legal as any other rifle, and can be bought at any gun store. Some states have Assualt weapon bans, which do not ban the actual rifle, but restrict 30rd magazines, and some cosmetic feature such as bayonet mounts and flash hiders from being on the rifle. Now Military full-auto machine guns are an all together different matter, they are legal in most states, but the paper work is through the Federal Governmet. There is no Class 3 license to own machine guns, all one needs is to pass a FBI background check, then apply for a Federal tax stamp and paper work, then find a person who is willing to sell you a MG. The problem is MGs were offically banned from civilian ownership in 1986, but previous owned MGs were grandfathered into the law. That means no newly manufactured MGs can be bought by civilians. The only legal MGs are ones that were leaglly owned by someone before the 1986 ban. That means there are only a finite amount of MGs for sale. That is why the prices are exteremly high. Starting price for a simple full auto SMG is about $3000USD, and prices go up to over $100,000USD for some rare MGs. Some states do regulate MGs ownership under their own laws. So the conclusion is that Semi-auto Assualt rifles, are perfectly legal in all states, but full auto military MGs are restricted by the Federal government and states to people who jump through all the legal hurtles.

Correction from my post above. The shooter did not have a girlfriend. It seems he was a loner with few, if any friends.