Mr. Ambler... there's already a ban on possession of automatic weapons.  It's found in both the National Firearms Act of 1934 and the Firearm Owner's Protection Act of 1968.  The only way a private citizen can possess an automatic weapon is by paying a very substantial tax, undergoing a full FBI background investigation, including photos and fingerprints, and registering the firearm with the BATF&E.  No such information about this particular shooter has come to light.  That means he (a) acquired automatic weapons illegally; (b) illegally modified semi-automatic weapons; or (c) used a device called a "Bump Fire."  That's a device which attaches to the stock of the weapon and uses the recoil of one shot to mechanically pull the trigger for the next, approaching the weapons cyclic rate of fire... much faster than human reactions and muscle control could.  Up until now, the BATF&E has determined this device to be legal, although I suspect, if used here, it will soon be made illegal.