The comments are at the center of a lawsuit, filed by landfill owner Fred Heebe.
Heebe claims Mann used the handle “eweman” to post comments that were defamatory about Heebe and his family.
Heebe is at the center of a federal investigation.
He already filed a similar lawsuit against another federal prosecutor, Sal Perricone, who resigned his position.
Letten says Mann is now no longer in any supervisory positions in his office.