I'd have to look at their disaster plan to be sure, but I think the Superdome is a designated spot (had been used at least twice before), the Convention center just happened when people fled the chaos of the superdome, and police? Hell, most of them never reported, some of the ones who did were downtown looting, and those who stuck to their posts were completely overwhelmed.
How many years in office did Nagin have to shape up the NOPD?