The person upon whom the writ has been served, whether it is directed to him or not, shall file a written answer, signed and sworn to by him stating whether he has custody of the person named in the writ. If the person is in his custody, he shall produce him and state in his answer his authority for holding the person in custody. If the custody is by virtue of a court order, the document in the possession of the custodian shall be annexed to the answer. The answer and the production of the person in custody shall be made at the place and time designated by the writ.