(a) Rule of Privilege. The United States or a state or subdivision thereof has a privilege to refuse to disclose the identity of a person who has furnished information relating to or assisting in an investigation of a possible violation of a law to a law enforcement officer or member of a legislative committee or its staff conducting an investigation.
(b) Who May Claim. The privilege may be claimed by an appropriate representative of the public entity to which the information was furnished.
(c) Exceptions.
(1) Voluntary Disclosure; Informer a Witness. No privilege exists under this rule (A) if the identity of the informer or the informer's interest in the subject matter of his or her communication has been disclosed by a holder of the privilege or by