At this point, the BG has armed robbery, kidnapping and agg. assault against him, and potentially has a hostage. There isnt a grand jury in the world that will indict you for shooting him at this point. I hope that trigger is extra smooth and the Tax Law section is close to the register, coz those books will be the best cover you have. I'd pick a good chance when he's distracted to throw a book and make noise at the other end of the store to get him away from pregnant lady, then make my move.