There have been several fraud cases filed resulting from alleged Katrina scams. In both Houston and Atlanta there have been cases involving allegations of the filing of false claims with FEMA. (see here and here). 

The St. Pete Times reports of a case of a Floridian being charged with fraud via the internet for allegedly using the Katrina storm to obtain money over the web for his own benefit when the money sought was to be used to assist hurricane victims. (see here).  This case uses the wire fraud statute as the basis for the charges.

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