(1) The commission or any committee of the commission authorized by the commission to do so may investigate the financial transactions of any office or department of the municipal government and the official acts of any municipal official and by similar investigations may secure information upon any matter.
(2) In conducting investigations, the commission or committee may compel the attendance of witnesses and the production of books, papers, and other evidence and for that purpose may issue subpoenas or attachments, which must be signed by the presiding officer of the commission or the presiding officer of the committee. The subpoenas or attachments may be served and executed by any officer authorized by law to serve subpoenas or other process. A witness may not be excused from testifying concerning the witness's knowledge of the matter under investigation in any inquiry, but the testimony may not be used against the witness in any criminal prosecution except for perjury committed upon the inquiry.