Wis. Stat. § 885.24: Actions for public moneys, immunity.

(1) No witness or party in an action brought upon the bond of a public officer, or in an action by the state or any municipality to recover public money received by or deposited with the defendant, or in any action, proceeding or examination, instituted by or in behalf of the state or any municipality, involving the official conduct of any officer thereof, may be excused from testifying on the ground that his or her testimony may expose him or her to prosecution for any crime or forfeiture. No person may be prosecuted or subjected to any penalty or forfeiture for or on account of testifying or producing evidence, documentary or otherwise, in the action, proceeding or examination, except a prosecution for perjury committed in giving the testimony.

(2) The immunity provided under sub. (1) is subject to the restrictions under s. 972.085.