42 Pa.C.S. § 6504: Return on writ.

The writ, or the order to show cause why the writ should not issue, shall be directed to the person having custody of the person detained. It shall be returned within three days unless for good cause additional time, not exceeding 20 days, is allowed. The person to whom the writ or the order is directed shall make a return certifying the true cause of the detention and, except as otherwise prescribed by general rules or by rule or order of court, shall produce at the hearing the body of the person detained.