Section 24. (a) Whenever the attorney general has reasonable cause to believe that a person, including any public body and any other state, regional, county, municipal or other governmental official or entity, has violated the open meeting law, the attorney general may conduct an investigation to ascertain whether in fact such person has violated the open meeting law. Upon notification of an investigation, any person, public body or any other state, regional, county, municipal or other governmental official or entity who is the subject of an investigation, shall make all information necessary to conduct such investigation available to the attorney general. In the event that the person, public body or any other state, regional, county, municipal or other governmental official or entity being investigated does not voluntarily provide relevant information to the attorney general within 30 days of receiving notice of the investigation, the attorney general may: (1) take testimony under oath concerning such alleged violation of the open meeting law; (2) examine or cause to be examined any documentary material of whatever nature relevant to such alleged violation of the open meeting law; and (3) require attendance during such examination of documentary material of any person having knowledge of the documentary material and take testimony under oath or acknowledgment in respect of any such documentary material. Such testimony and examination shall take place in the county where such person resides or has a place of business or, if the parties consent or such person is a nonresident or has no place of business within the commonwealth, in Suffolk county.

(b) Notice of the time, place and cause of such taking of testimony, examination or attendance shall be given by the attorney general at least 10 days prior to the date of such taking of testimony or examination.

(c) Service of any such notice may be made by: (1) delivering a duly-executed copy to the person to be served or to a partner or to any officer or agent authorized by appointment or by law to receive service of process on behalf of such person; (2) delivering a duly-executed copy to the principal place of business in the commonwealth of the person to be served; or (3) mailing by registered or certified mail a duly-executed copy addressed to the person to be served at the principal place of business in the commonwealth or, if said person has no place of business in the commonwealth, to his principal office or place of business.

(d) Each such notice shall: (1) state the time and place for the taking of testimony or the examination and the name and address of each person to be examined, if known and, if the name is not known, a general description sufficient to identify him or the particular class or group to which he belongs; (2) state the statute and section thereof, the alleged violation of which is under investigation and the general subject matter of the investigation; (3) describe the class or classes of documentary material to be produced thereunder with reasonable specificity, so as fairly to indicate the material demanded; (4) prescribe a return date within which the documentary material is to be produced; and (5) identify the members of the attorney general's staff to whom such documentary material is to be made available for inspection and copying.

(e) No such notice shall contain any requirement which would be unreasonable or improper if contained in a subpoena duces tecum issued by a court of the commonwealth or require the disclosure of any documentary material which would be privileged, or which for any other reason would not be required by a subpoena duces tecum issued by a court of the commonwealth.

(f) Any documentary material or other information produced by any person pursuant to this section shall not, unless otherwise ordered by a court of the commonwealth for good cause shown, be disclosed to any person other than the authorized agent or representative of the attorney general, unless with the consent of the person producing the same; provided, however, that such material or information may be disclosed by the attorney general in court pleadings or other papers filed in court.

(g) At any time prior to the date specified in the notice, or within 21 days after the notice has been served, whichever period is shorter, the court may, upon motion for good cause shown, extend such reporting date or modify or set aside such demand or grant a protective order in accordance with the standards set forth in Rule 26(c) of the Massachusetts Rules of Civil Procedure. The motion may be filed in the superior court of the county in which the person served resides or has his usual place of business or in Suffolk county. This section shall not be applicable to any criminal proceeding nor shall information obtained under the authority of this section be admissible in evidence in any criminal prosecution for substantially identical transactions.