Updated Friday, December 7, 2012 at 12:16 AM
NEW ORLEANS — New Orleans' corruption-busting federal prosecutor resigned Thursday after two top deputies became embroiled in a scandal that threatens to undermine some of his biggest cases and damaged his standing as one of the most popular public officials in a city with a rich history of graft.
U.S. Attorney Jim Letten, whose successful prosecution of a former Louisiana governor and numerous other officials won him bipartisan praise for more than a decade, had been under mounting pressure ever since two veteran prosecutors admitted anonymously posting criticism of judges and comments about cases on a newspaper website.
At a news conference, Letten, 59, gave no reason for his resignation, effective next Tuesday, but said the decision "was ultimately mine."
Despite the dearth of details, everyone knew why he was stepping aside.
Beginning last spring, a series of legal motions had revealed that Letten's senior prosecutors had been making provocative, even pugnacious, comments about active criminal matters and other subjects under aliases at nola.com, the website of The Times-Picayune.
For a team of prosecutors once referred to in the news media as the Untouchables, with a chief who had drawn broad enough popularity that he had survived a party change in the White House, the exposures were stunning.
Last month, the revelations of online misconduct reached Letten's top assistant, Jan Mann. A federal judge, in a scathing 50-page order, broached the possibility of criminal conduct in regard to her online activities, as well as those of another senior prosecutor, Sal Perricone, who resigned in March.
The judge also revealed that another federal prosecutor had expressed suspicions about the comments to his supervisors in 2010.
The exposure of Mann, months after Letten's avowals that Perricone had acted alone, raised doubts about the effectiveness of an internal investigation by the Justice Department.
The revelations could also jeopardize hard-fought convictions — including those last year of police officers involved in post-Katrina killings on the Danziger Bridge — and continuing inquiries such as a bribery investigation that appears to be steadily encircling C. Ray Nagin, the former mayor.
Letten has maintained he knew nothing about his subordinates' online activities, and there has been no evidence to contradict that. But the problems were beginning to stack up, as he acknowledged Thursday.
"It is essential that the challenges which we take on, and especially our current challenges ... never, ever, ever, under any circumstances threaten to divert or distract us from our sacred mission of protecting the freedom, the property, the lives and the quality of lives of all of our people," he said.
Sen. Mary Landrieu, D-La., commended Letten's "record of rooting out public corruption" but called the decision "a necessary step."
The Department of Justice announced an interim replacement Thursday and named a federal prosecutor from Georgia who will be restarting the investigation into the office's internal problems.
Letten, who has worked in federal law enforcement for nearly three decades, began in his current office as an interim appointment in 2001.
He was well-known, having led the successful prosecution of former Gov. Edwin Edwards on bribery and racketeering charges. (Letten named his dog Rico, after the federal racketeering statute.)
Letten focused on public corruption, a fat target in Louisiana's Eastern District; the FBI office in New Orleans was one of only two in the country to have three public-corruption squads.
Letten successfully prosecuted parish presidents for bribery, sheriffs for mail fraud, mayors for tax evasion, housing-agency officials for embezzlement and contractors for all kinds of things.
If Letten was seen by many as the good cop, Perricone and Mann were seen as the other cops. Both were known and at times criticized for their aggressiveness (Perricone once shoved a defense lawyer after a losing an argument in a judge's chambers.). The now-exposed online commentary of the two — which ripped judges, defendants, fellow prosecutors and politicians, including Obama — seems to corroborate those reputations.
Material from The Associated Press is included in this report.
Jim Letten, U.S. Attorney for the Eastern District, announces his resignation Thursday in New Orleans.