Mont. Code Ann. § 26-2-103

If a witness is concealed in a building or vessel so as to prevent the service of a subpoena upon the witness, any court, judge, or any officer issuing a subpoena may, upon proof by affidavit of the concealment and of the materiality of the witness, make an order that the sheriff of the county serve the subpoena, and the sheriff shall serve it accordingly and, for that purpose, may break into the building or vessel where the witness is concealed.