Section 2A. The clerk of the courts in any county, or in Suffolk county the clerk of the superior court for criminal business, shall, upon written request of the attorney general accompanied by a certificate that public necessity requires such action, signed by the chief justice of the superior court, issue writs of venire facias for forty-five veniremen of whom the court shall select twenty-three for service as a special grand jury to hear, consider and report on such matters as the attorney general may present. Said jurors shall serve for a period of six months, unless sooner discharged by the attorney general or by the said chief justice, and shall be drawn, summoned and returned in the same manner, and shall have the same powers and receive the same compensation, as grand jurors summoned for service under sections one and two, and the provisions of sections three to fourteen, so far as apt, shall apply to such jurors. In Middlesex county, the clerk of the courts shall send a letter of venire to the jury commissioner as set forth in section twelve of chapter two hundred and thirty-four A.