The Washington Post reported that during a federal investigation regarding a landfill owner, apparently two federal prosecutors used aliases to posted anonymous comments. Fred Heebe (he landfill owner under investigation) filed a defamation lawsuit based on the anonymous postings and hired a former FBI agent to find the posters. The former FBI agent James R. Fitzgerald (who helped find the Unabomber in 1996) analyzed 598 anonymous postings. The trail of postings led to former US attorney Sal Perricone. The Washington Post went on to say:

Perricone admitted posting the derogatory information and making similar attacks on attorneys, defendants, police officials and judges. He resigned and remains under investigation by the Justice Department.

Heebe filed a second lawsuit against another prosecutor Jan Mann: 

The suit accused her of anonymously posting disparaging comments about Heebe on the Times-Picayune Web site, in some cases coordinating her comments with Perricone’s.

As a result of these revelations, after 11 years as the chief prosecutor, Jim Letten resigned as the US attorney for the Eastern District of Louisiana in New Orleans.

It’s hard to image that prosecutors would anonymously post critical comments of individuals under investigation, but given the facts we may now see revelations about other such anonymous postings by prosecutors in other jurisdictions.