(a) Before Submission to the Jury. After the government closes its evidence or after the close of all the evidence, the court on the defendant's motion must enter a judgment of acquittal of any offense for which the evidence is insufficient to sustain a conviction. The court may on its own consider whether the evidence is insufficient to sustain a conviction. If the court denies a motion for a judgment of acquittal at the close of the government's evidence, the defendant may offer evidence wi...