16 Pa. Stat. § 4441
The district attorney of the county may, with the approval of the salary board, whenever the court of quarter sessions and district attorney may deem it necessary for a particular and temporary assignment, appoint a special detective, whose duty it shall be to assist in obtaining such evidence as shall be directed by the district attorney for the Commonwealth, and perform such other duties as the court may direct. He shall be allowed expenses necessarily and actually incurred in the performance of his duties.
Such special detective officer shall be a general police officer and shall have all the powers that are conferred on constables by the existing laws of this Commonwealth, so far as they relate to crimes or criminal procedure.
16 P.S. § 4441