Human Rights Watch offers "Prisoners Abandoned to Floodwaters". They claim that Orleans Sheriff's Department officers abandoned prisoners who were locked in the Templeman III building in the jail compound in New Orleans:
"Of all the nightmares during Hurricane Katrina, this must be one of the worst," said Corinne Carey, researcher from Human Rights Watch. "Prisoners were abandoned in their cells without food or water for days as floodwaters rose toward the ceiling."
They also say that there are 517 unaccounted-for prisoners. Some of those might have escaped, but others might not have...
The article "A night in New Orleans jail turns into month of misery for 2 Ohio men" has the accounts of two tourists who were arrested for misdemeanor disorderly conduct... on the Friday before the hurricane. That resulted in them being in the situation described above.
Expect this story to get more attention as more accounts are published and when the status of the 517 is determined.