He could steal one. He could borrow one from a friend. Neither federal nor Ohio law regulates private sales. Only licensed gun dealers must do background checks. Hundreds of thousands of gun transactions nationwide are made privately each year, with no background checks, and no record kept.
People sell guns privately at gun shows, over the Internet, through newspaper ads.
Some states regulate them. The seller may know nothing about the buyer's background. Even if the seller knows the buyer is ineligible to buy a gun, which would make the seller's action a felony, the violation would likely be undetectable. Then there are the straw men, who lie on ATF form 4473, stating they are buying the guns for themselves. After the purchase, they turn the guns over to criminals for profit.