Of the city’s airport, he said in his first campaign that the city should “sell that sucker,” and many applauded his moxie. That he turned out to be much more adept at proposing big ideas than following through with them was something he acknowledged, and it became one of the qualities that most infuriated New Orleanians in the years following Katrina.

During his time on the witness stand, Mr. Nagin brought up Katrina several times, talking about how much work there was to be done in the recovery, how demanding his job was and how much pressure was put on the daily business of the city. But prosecutors turned this around, asking Mr. Nagin how he could eat expensive meals on the city credit card, or help a businessman get rid of steep tax bills in return for a trip on a private jet, when residents were hurting so badly. They also pointed out that some of the schemes predated the storm and continued after he left office in 2010.

Gary Clark, a political science professor at Dillard University in New Orleans, who as a Civil Service commissioner dealt with the mayor, dismissed any notion that the mayor did not know what he was doing.

“He’s a shrewd tactician,” he said of Mr. Nagin, pointing out how adeptly he had shifted from a largely white constituency in 2002 to largely black one in 2006. “You don’t win the mayorship of New Orleans by being naïve.”

Still, the inattention to detail for which Mr. Nagin was known seemed to form a part of his defense at trial.

From the witness stand, he testified that the extensive paper trail on which much of the case rested — calendar entries, tax filings, legal documents and city paperwork — was mostly handled by others, like accountants or assistants. His lawyer asked whether a person taking bribes would really be so careless as to leave such a record, behavior that brazenly flouts the wisdom shared by a former Louisiana governor, Earl K. Long: that one should never put in writing what one can convey in a smile, a nod or a wink.

Those who knew him say it is unsurprising.

“I think he may have been reckless,” said Oliver Thomas, a city councilman during Mr. Nagin’s term who pleaded guilty to taking a bribe in 2007.