Corrected entry: The Joker publicly announces on television that he will be throwing a huge parade through the streets of the city. So this would be a great opportunity for the police department to apprehend the Joker and his henchmen. Instead, when the parade takes place there is not one police officer seen anywhere.
mightymick
23rd Jul 2012
Correction: The joker doesn't announce where the parade was, and from the reactions of the police officers in the bar when he announces this suggests they'd be more interested in getting some money than stopping the Joker.