He did not address the allegations against his underlings. But he previously said he had no idea what they were up to until their online activities were revealed in court filings.
Until recently, Letten, a Republican-appointed holdover who has held the post since 2001, appeared to be a lock to keep his job during President Barack Obama's second term. Instead, his departure ends his tenure as the nation's longest-serving U.S. attorney.
Letten won fame as an assistant U.S. attorney when he secured a racketeering conviction of former Gov. Edwin Edwards in 2000. His office also successfully prosecuted corrupt judges, killer police officers, bribe-taking school officials and post-Katrina scam artists.
"The public perception of Jim Letten really transcended the position of United States attorney," said Rafael Goyeneche, director of the Metropolitan Crime Commission of New Orleans, a watchdog group. "In many respects, he is the public face of what the people of Louisiana want to change about the pre-Katrina ways of doing business in Louisiana."
Dana Boente, a first assistant U.S. attorney in Virginia, was appointed to Letten's post in the interim.
Letten's downfall was set in motion when one of his prosecutors, Sal Perricone, resigned in March after acknowledging he criticized judges and politicians and commented on cases in anonymous posts on The Times-Picayune's website.
Among other things, Perricone described a federal judge in New Orleans as someone who "loves killers," and charged that "Obama and his West Wing band of Bolsheviks have a master design to strangle America's economy."
Then, last month, Letten demoted his top assistant, Jan Mann, after she, too, confessed to posting anonymous comments on the site.
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."