Kim, could you say that the action was captured on a store surveillance videotape that someone was playing over at the end of the night? You could use that as the reason you would like to spend some time with these people *one on one* and strongly stress to him how terribly wrong his behavior was and offer alternatives. This might make him a little less hostile than if he thought he was being attacked by a particular store employee.
You must just feel awful. I would too and would have probably laid in bed last night and worried about that poor dog and her future. :( Poor Holly, she deserves better than that. Please update us and let us know how this goes. *sigh*