. >> narrator: sam walker is a professor of criminal justice and an expert on the legal standards forwhen police can use their guns. >> the standards on deadly force are fairly clear. an officer can use deadly force where there is a threat to someone's life, or that this person is armed and fleeing and likely to commit another armed offense. that's a very narrow range. >> narrator: but in post-katrina new orleans, nothing was clear. could stealing food, water or a tv now mean a death sentence? >> a shoot to kill order, to shoot looters, would violate the long-established standards on use of deadly force. >> narrator: orders to the nopd rank and file became even more uncertain when mayor nagin called for martial law. it was the day after the storm and he had just been told by his chief of police that a police officer had been shot in the head. this story, we now know, was true. >> our police, at that point, were completely focused on search and rescue. and here they were being shot at. and it made the mayor furious. and that's when he said, we need to declare martial law. >> the city t