Roger,
That is a good question which I have pondered since reading it the other night. Did Johnson believe that he might be arrested as an accomplice? Also, if Jerry is correct and he had issued passes to Booth and Herold (which I now believe was a good possibility) what happened to the passes? Would protocol have had Sgt. Cobb collecting the passes and turning them in, or would he have merely examined them and returned them to their owners?