The attorney general and reporter, the district attorneys general, county attorneys, and city attorneys have the power and they are hereby directed, whenever complaint has been made, and the names of the witnesses furnished them, or whenever they deem necessary, to issue subpoenas for such witnesses so furnished them and for such persons as they shall have reason to believe have any knowledge of the complaint made, to appear before the attorney general and reporter, district attorney general, county attorney, or city attorney, at a time and place to be designated in the subpoena then and there to testify concerning the subject matter set out in the complaint.