If he EASILY bought one, he violated the law. Full-auto weapons cannot be purchased in the USA without a full and detailed background check, an ATF license costing $250, a designated, licensed gun dealer who will take possession of the weapon at your death, and you can't actually own a NEW one, so you have to buy an OLD automatic weapon, which in good condition will cost you 10-20x what an actual new one will due to the market forces.

That ain't easy.

So if we can't enforce the laws that already exist, what makes anyone think new laws will make a difference? The new ones will magically be enforced better?