NEW ORLEANS — Allegations of prosecutorial misconduct tainted a Justice Department inquiry into the source of leaked information about the probe of deadly police shootings on a New Orleans bridge after Hurricane Katrina, a federal judge said Monday.

U.S. District Judge Kurt Engelhardt ordered the Justice Department to conduct a new investigation of news reports that said a former police officer was going to plead guilty when the case was under seal.

Engelhardt initially called for an investigation in June. But he said a report submitted by Jan Mann, U.S. Attorney Jim Letten’s former top lieutenant, is tainted and must be redone.

Letten demoted Mann earlier this month for anonymously posting comments on a newspaper’s website about a south Louisiana landfill owner who is the target of a probe by Letten’s office.

Engelhardt said the Justice Department should consider appointing an independent counsel to review the activities of Mann and former Assistant U.S. Attorney Sal Perricone, who resigned in March after acknowledging he criticized judges and politicians and commented on cases in anonymous posts on

“First of all, having the DOJ investigate itself will likely only yield a delayed yet unconvincing result in which no confidence can rest,” Engelhardt wrote.

A different judge had called for an investigation after The Associated Press and The Times-Picayune newspaper reported Feb. 23, 2010, that former Lt. Michael Lohman was expected to plead guilty in the case the following day to participating in a cover-up of the Danziger Bridge shootings.

Engelhardt said the Justice Department has failed to formally question “media recipients” of information about the case against Michael Lohman. In his order Monday, he said prosecutors must ask these recipients about the sources of their information or else state in writing why they won’t.

Engelhardt presided over a trial that resulted in the convictions of five former officers. Defense attorneys have asked Engelhardt to order a new trial, arguing that a series of leaks to the media, including about Lohman’s guilty plea, deprived their clients of a fair trial.

Engelhardt said their request is “still a longshot in terms of relief” but isn’t frivolous and merits further inquiry.

“Prosecutorial misconduct in this case is a very near and present thing; however, the possibility of it ripening into grounds for relief remain somewhat distant,” he wrote.

Police officers shot and killed two unarmed people and wounded four others on the bridge less than a week after the storm’s landfall in August 2005. The five officers convicted at trial were sentenced in April to prison terms ranging from six to 65 years. Five other former officers, including Lohman, have pleaded guilty to participating in the cover-up and are serving prison sentences.