If the court of common pleas and district attorney deem it necessary for a particular and temporary assignment, the district attorney of a county, with the approval of the county salary board, may appoint a special detective, whose duty it shall be to assist in obtaining evidence as directed by the district attorney for the Commonwealth and to perform other duties as the court may direct. The special detective shall be:
(1) Allowed expenses necessarily and actually incurred in the performance of duties.
(2) A general police officer and have all the powers that are conferred on constables under the existing laws of this Commonwealth relating to crimes or criminal procedure.