Deputies' Online Misconduct Behind U.S. Attorney Jim Letten's Abrupt Resignation?

Online misconduct by his top deputies may have brought down the nation's longest-serving U.S. attorney, Jim Letten.

Letten is credited with convictions of corrupt New Orleans judges, killer police officers, and bribe-taking officials in Hurricane Katrina’s wake. He notably secured the racketeering prosecution of former Louisiana Gov. Edwin Edwards in 2000.

Letten abruptly resigned on Thursday while the Justice Department investigates claims that his lieutenants criticized judges and politicians and commented on cases in anonymous posts on a newspaper's website.

The Justice Department's Office of Professional Responsibility is investigating the online activities of the two veteran prosecutors in his office, the Associated Press reported.

Sal Perricone resigned in March after acknowledging the anonymous posts and Letten demoted his top assistant, Jan Mann, last month after she also confessed to posting anonymous comments on the same site.

The two were unmasked in court filings by attorneys for a New Orleans businessman whose landfill operations are the subject of a federal probe.

Letten didn't touch on the allegations against his deputies during a news conference. He previously said that he had no idea what his deputies were doing until the online activity was revealed in the court filings. He said the decision to resign came after discussions with colleagues, Justice Department officials and his family.

Dana Boente, the first assistant U.S. attorney for the Eastern District of Virginia, was appointed in the interim. Attorney General Eric Holder said in a statement that Letten has been a "valued partner, dedicated public servant and a good friend."

Letten is stepping down as the attorney's office is building up an investigation of former New Orleans Mayor Ray Nagin's administration. Letten's office had already secured guilty pleas by two businessmen who admitted that they bribed an unidentified city official during Nagin's time in office. It also has threatened to hurt the government's pursuit of other high-profile cases.