That a grand jury shall consist of twelve citizens, any nine of whom concurring may find an indictment or a true bill: Provided, that no grand jury shall be convened except upon an order of a judge of a court having the power to try and determine felonies; but when so assembled such grand jury shall have power to investigate and return indictments for all character and grades of crime; and that the power of grand juries to inquire into the willful misconduct in office of public officers, and to find indictments in connection therewith, shall never be suspended.