Lock the Doors.

When NASA has had its two Shuttle accidents, at one point the Flight Director orders the doors to Mission Control to be locked: no one goes in or out until all the data of the flight has been secured. It is essential for a successful accident investigation.

The same should hold true for all of the data pertaining to the Katrina Catastrophe. Let's not have any city, state, or federal documents that pertain to the planning and preparations for this disaster to suddenly come up "missing".
For example, the City of New Orleans' disaster plan...(courtesy Bush in a Tree)