The court of appeals may convene a grand jury under section 7c with jurisdiction over 2 or more counties in this state if a petition is properly filed under section 7b, and all of the following circumstances exist:

  (a) The petition establishes probable cause to believe that a crime, or a portion of that crime, has been committed in 2 or more of the counties named in the petition.

  (b) The petition establishes reason to believe that a grand jury with jurisdiction over 2 or more of the counties named in the petition could more effectively address the criminal activity referred to in the petition than could a grand jury with jurisdiction over 1 of those counties.