I'm sure that they have staked out high ground; second or third floor spaces where they are hoarding their booty. When the true evacuation occurs, the looters, for the most part will try to stay, ignoring the official calls to leave. At that point, many of them will likely die off; victims of their own incompetence, of nature, or finally of starvation. After the evacuation, the NG can grab them as they pop up, as anyone left who is not with the relief effort is there for looting and should be tossed in the hoosegow (or more preferentially shot).
The sheriff in Biloxi made more sense to me this morning -- he went on local radio there and said, "We've got a jail. It's got no power, it's hot, it's uncomfortable and it's already full. I've got no problem with stacking more folks in there, even in the hallways if I have to. You loot, I'm gonna put you in there. Period."
On WWL they just said looters are now breaking into houses on St. Charles. Bad enough they have the flooding which is devastating but now people have to put up with looters breaking into their homes. Disgusting.