As I understand the evidence in that case: No gun legally purchased at a gun show.....The teen psycho's at Columbine were not old enough to purchase guns, legally, on their own. They were armed by a friend that made a "straw purchase". That means the "friend" lied that the guns were for themself, making those guns illegally purchased. Any firearm purchased through a Federal Firearms License holding gun dealer is required by law to do an FBI backround check as part of that transaction, whether at a gun show or in a store front. The only purchases currently exempted from the backround check are private individual to private individual.