NOBODY would lock me in if there was shooting in a mall. NOBODY. Not without giving up a few inches of skin, or worse. I would be leaving, and I don't give a damn what their security, the cops, or anybody thought. Not staying at the wrong end of a shooting range. Period.
Maybe, just maybe, they are SAFER behind the locked, steel door of a mall backroom than running (and being a target) for the exit?