During pushback, the ground crew are responsible for the A/C. On the ground, parked or at any other stage of flight, the Captain is responsible. Therefore I can not see how the local police (who are not on board the a/C) can tell a Captain not to evacuate. Would you sit on a bomb for 2 hrs? What if there was a bomb and it did go off? Who would have been at fault? Would the press/everyone have blamed the crew by quoting chapter and verse of the ANO/JAR OPS? Obviously I don't know all of the facts, but given half the chance, I would have evacuated. I actually had the same scenario in the simulator not long ago.