What actually happened and who is culpable in these incidents is now the focus of probes by the US Attorney's Office and the FBI. Asked why investigations like these are just now being launched, New Orleans Mayor Ray Nagin recently explained, "We had a little event called Katrina."

Some New Orleanians believe the allegations point to "a broader pattern of violence ... that should reframe our understanding of the catastrophe," writes A.C. Thompson, a reporter with ProPublica, a nonprofit journalism venture.

In an article published in The Nation, a weekly news magazine, he claims that incidents of white-on-black violence "have gone unpunished."

But teasing the facts out of a flood of rumor and grains of truth will be daunting. It is a "morally treacherous" gambit to measure the actions of stressed people in the virtually lawless state of post-Katrina New Orleans by typical standards, says Peter Scharf, a criminologist at Tulane University. The outcome, he worries, could impact t