NEW : Each died of a single gunshot wound to the head , medical officer 's report says . Two sisters of Iowa state senator John Smith were found shot to death Friday . Iowa police have n't identified a motive for the shootings .
NEW : Each died of a single gunshot wound to the head , medical examiner 's office says . Two sisters of Iowa state Rep. Mary Wolfe were found shot to death Friday . Pittsburgh police have n't identified a motive for the shootings .