Commenting to # 12, it's actually required by most companies to close the store down after a robbery to call the police and to prevent the robber from coming back. And in Canada and the US it would be against the law to dock her hours after closing the store due to an extremely stressful situation such as a robbery.
OP, call the labor board, or human ressources and file a complaint.
I know it sucks but I agree with your boss. You didn't work those two and a half hours. If you stayed around, talking to police, etc. for the rest of your shift then fine. If you closed the store because you were upset... then no. I wouldn't pay you if say, you left because your dog died. So I wouldn't pay you if you were too upset to work. It sucks, sure, but don't expect free money.