Psycho criminal mass murderers don't usually obey gun laws.

In the state of Ohio, he illegally turned that into a machine gun. Inserting a magazine greater than 30 rounds instantly classifies it as an "automatic firearm"

In the State of Ohio:

"'Automatic firearm' means any firearm designed or specially adapted to fire a succession of cartridges with a single function of the trigger. 'Automatic firearm' also means any semi-automatic firearm designed or specially adapted to fire more than thirty-one cartridges without reloading, other than a firearm chambering only .22 caliber short, long, or long-rifle cartridges."