No person shall be excused from testifying before the attorney general and reporter, district attorney general, county attorney, or city attorney, at such investigation, or in any investigation, or be excused from testifying in any proceeding brought in any court of competent jurisdiction, under this chapter, on the ground that such person's testimony may incriminate such person; but no person shall be prosecuted or punished on account of any transaction, matter, or thing concerning which such person shall be compelled to testify, nor shall such testimony be used against such person in prosecutions for any crime or misdemeanor under the laws of this state.