Because of inadmissible evidence shown to jurors, the judge in the Roger Clemens perjury trial has declared a mistrial. U. S._ District Judge Reggie Walton made his ruling after prosecutors made statements not once, but twice about evidence that Walton had previously ruled inadmissible. Prosecutors argued that Walton could simply tell the jury to disregard what had been said, but Walton said it was too late. Now the question is [...]