That's basically what the mayor of Baton Rouge (who is black) also said. No racism involved, just acknowledgement that there are criminal aspects to some of those that may be leaving NO.
I would imagine that this is why the transport was halted at the Dome and started up at the Convention Center. They've identified the hard cases and made sure they didn't get loaded up to go to the shelters. The 5,000 that are remaining at the Dome will be among the last out of NO. There is some crude pre-screening going on (perhaps identified by the people in the Dome). I think the same will happen elsewhere. One of the good things about the looting footage is that those people will be identified and put in places that won't be too pleasant for them with an awful lot of security.
I also think they didn't want to take people out of the Convention Center till they could search them, and that's the first thing I noticed this morning, before getting on a helicopter, they're searched and patted down.