Exemption from arrest and service of process. If a witness from another state comes into or passes through this Commonwealth under

§ 5979.  Exemption from arrest and service of process. If a witness from another state comes into or passes through this Commonwealth under an order directing him to attend and testify in this or another state, he shall not, while in this Commonwealth pursuant to the order, be subject to arrest or the service of process, civil or criminal, because of any act committed prior to his arrival in this Commonwealth under the order.