Sandra Kemper, a suspect in an alleged arson that took the life of her son, denied nine times that she had anything to do with the fire. Then the St. Louis County police detective resorted to one of the oldest tricks in the book -- he told Kemper that she had failed a lie detector test. Later that day, Kemper admitted that she set the fire to get out from under the burden of being the sole provider to her family and to collect insurance proceeds. But the confession did not fit the facts of the crime, the motive evidence was weak, and Sandra had passed the lie detector test with flying colors. In pre-trial motions, Sandra's counsel succeeded in convincing the judge to allow him to call a polygraph expert to both verify that Sandra had passed and to comment on the unprofessional nature of the polygraph exam. The theory being that the way in which the polygraph was conducted was part of the "totality of circumstances" necessary for the jury to determine if the confession was voluntary and trustworthy. Then, at trial, the judge reversed himself after the evidence was admitted and declared a mistrial. Earlier this week in State ex. rel Kemper v Vincent, No. SC87246, the Missouri Supreme Court held that the trial court should have allowed the evidence that Kemper passed into evidence under the "rule of completeness," an evidentiary rule that holds that a party may introduce evidence of the circumstances of a conversation, writing, or statement to enable the jury to have a complete picture." Better yet for Kemper, the Court held that double jeopardy prohibited the State from retrying her. Where the defense opposes a mistrial, double jeopardy bars a retrial unless there was a"manifest necessity" for the mistrial. Since the trial judge's basis was error as a matter of law, no such necessity existed. End of story.