Iowa Code § 810.16: Disposition of evidence.

If at the time of the return probable cause does not exist to believe that the person committed the felony specified in the application, the court shall order that the products of the nontestimonial identification procedures and all copies thereof, be promptly destroyed. Upon motion of the prosecuting attorney, the court may authorize further retention of the nontestimonial evidence so obtained for such time as reasonably necessary to facilitate a continuing investigation or prosecution.