The Justice Department's Office of Professional Responsibility is investigating the postings, which defense attorneys have cited as evidence the prosecutors improperly tried to influence cases.
The authors of the posts were unmasked in court filings by attorneys for New Orleans businessman Fred Heebe, whose landfill operations are under federal investigation. Heebe had been nominated by then-President George W. Bush for U.S. attorney in 2001 but withdrew amid allegations he had abused an ex-girlfriend and his ex-wife. He denied the allegations. Letten wound up with the job instead.
Letten is stepping down at a time when his office is ramping up an investigation of former New Orleans Mayor Ray Nagin's administration. The probe has resulted in guilty pleas by two businessmen who said they bribed an unidentified city official.
The misconduct allegations have provided ammunition for defense attorneys to challenge other high-profile prosecutions, including the conviction of five former New Orleans police officers on federal civil rights violations over a deadly shooting on a bridge after Hurricane Katrina in 2005.
Defense attorneys in the so-called Danziger Bridge case have asked for a new trial, arguing that the online posts and other media leaks were part of a campaign to smear the officers and possibly influence potential jurors.
On Thursday, Attorney General Eric Holder announced the appointment of John Horn, a first assistant U.S. attorney in Georgia, to investigate the online posts and leaks.
Edwards, the roguish, wisecracking former governor who was convicted of taking payoffs in return for casino licenses, reacted to Letten's downfall by alluding to the old adage about watching the bodies of one's enemies come floating down the river.
"Sit by the river long enough," he told Baton Rouge TV station WAFB. "I did."