You knew or should have known the buyer is a raging psychotic and was going to use the fully semi-automatics you sold him to murder those people...otherwise he would have bought from a dealer...he had the money so that is proof he was trying to avoid a background check. .he is absolutely correct, if you need absolute proof, so will the just deciding your fate, that simple act on your part to try to ensure laws were followed may have resulted in an innocent verdict. Or as a minimum, a mistrial, all it takes is one juror ro have doubt and little things like this can make that happen.