Private investigators and Attorney's who need to identify an informant, should check out this website.

"Who's A Rat is a database driven website designed to assist attorneys and criminal defendants with few resources. The purpose of this website is for individuals and attorneys to post, share and request any and all information that has been made public at some point to at least 1 person of the public prior to posting it on this site pertaining to local, state and federal Informants and Law Enforcement Officers. This includes an Informant who makes his or her Informant status known to any person."

Link: http://www.whosarat.com/