What kind of evacuation is it when 1/3 of the police force bails?
You say the poor had an option, evacuate or stay behind in potentially one of the worst flood prone areas of the city. That's not the correct option. The only option was to evacuate, and to have the mayor and Governor have a real plan for prtotecting these areas using their own police. When Nagin and his police shief allowed for the NOPD to dissolve they instantly failed their responsibilities.
First of all, the mayor of New Orleans does not have jurisdiction over the Orleans Parish Sheriff.
Second, this disaster is far too big for any state or local government to handle just as the 9/11 attack on the WTC was for NYC and NY State to handle.