Machine guns are already illegal.
Automatic weapons are not illegal to own under Federal law, but are heavily taxed & regulated.
However, in some states they are totally illegal to possess.
Please stop saying stupid stuff like machine guns are illegal. Maybe for you, if you live in a slave state like NO, MY, IL, M.D., MA, CA etc, but not for those of us in the free states, and not for the murderer. The ATF has not stated it was a machine gun, and I bet it wasn’t.