NEW ORLEANS, Nov. 9 - On a single day last June in Pigeon Town and Hollygrove, impoverished neighborhoods of worn frame houses at the city's western edge, four men were killed, adding to the eight already slain there this year. Young men brazenly sold drugs from street corners in broad daylight. The gunfire was constant. Residents were fearful.

But the bullets and the drugs and the fear are gone now, swept away by Hurricane Katrina, along with the dealers and gangs and most of the people.

There has not been a single killing in this violence-prone neighborhood, or anywhere else in New Orleans, since the chaos that immediately followed Hurricane Katrina subsided. New Orleans, the nation's most dangerous city, has suddenly become perhaps its safest, and what had easily been the country's murder capital now has a murder rate of exactly zero. Although several people were believed to have been killed in the disorder that followed the floods for several days, the last killing officially recorded by the police was on Aug. 27, two days before the hurricane hit. A bar owner was found shot to death that day in his establishment on Magazine Street.

And when the city was finally evacuated, the criminals left, too.

Since then some 60,000 to 80,000 residents have returned, a fraction of the city's previous population of 450,000. What is remarkable to criminologists, though, is how few criminals seem to be among them.