(a) A lawyer who has formerly represented a client in a matter shall not thereafter represent another person in the same or a substantially related matter in which that person's interests are materially adverse to the interests of the former client unless the former client gives informed consent, confirmed in writing.
(b) A lawyer shall not knowingly represent a person in the same or a substantially related matter in which a firm with which the lawyer formerly was associated had previously represented a client:
(1) whose interests are materially adverse to that person; and
(2) about whom the lawyer had acquired information protected by Rules 1.6 and 1.9(c) that is material to the matter; unless the former client gives informed consent, confirmed in writing.
(c) A lawyer who has formerly represented a client in a matter or whose present or former firm has formerly represented a client in a matter shall not thereafter:
(1) use information relating to the representation to the disadvantage of the former client except as these Rules would permit or require with respect to a client, or when the information has become generally known; or
(2) reveal information relating to the representation except as these Rules would permit or require with respect to a client.
Law firms and legal service organizations which handle a high volume of cases confront the limitations of this rule on a more frequent basis than do other practitioners. Firms and organizations may accept cases where a former client is a witness in the new (current client's) case if the representation of the former client is not “substantially related” to the current client’s case. Rule 1.9(a) permits such representation, but attorneys are cautioned to fully explore the definition of "substantially related" under relevant case law in the controlling jurisdiction. If such representation is permissible, attorneys in the law firm or organization must nevertheless take appropriate steps in a case that is not substantially related to comply with Rule 1.9(c) by protecting the confidential information obtained during the representation of the former client.
The New Hampshire Public Defender has adopted a Rule 1.9(c) compliance policy in cases that are not substantially related in which a “neutral attorney” orders the former client’s files sealed and prohibits any communication between the attorney who represented the former client and the attorney who represents the new client. In two cases where the State sought disqualification of the Public Defender because one of its attorneys had previously represented an individual who was a state's witness in the new case, the New Hampshire Superior Court denied disqualification and referenced with apparent approval the Public Defender's Rule 1.9(c) compliance policy. See State of New Hampshire v. Gordon Perry, Nos. 97-S-777 - 780 (MerrimackCounty Superior Court (Nadeau, J.) April 10, 1998); State of New Hampshire v. Eric Smalley, No. 01-S-1280 (MerrimackCounty Superior Court (McGuire, J.) January 29, 2002).