Hunter or Hunted

On the last day of deer hunting season, a woman is killed while walking her dogs in the woods. The victim has no enemies and her husband has an alibi, so police assume it was a hunting accident... until a strange letter turns up, allegedly written by the woman before her death. Police begin to wonder if the woman may have been the target all along, and a forensic document examiner, a slingshot, and an unusual physics experiment answer their question.