In a case tried by the court without a jury, a jury having been waived, the court on motion of the defendant or on its own motion shall order the entry of a judgment of acquittal of one or more of the offenses charged in the accusatory pleading after the evidence of the prosecution has been closed if the court, upon weighing the evidence then before it, finds the defendant not guilty of such offense or offenses. If such a motion for judgment of acquittal at the close of the evidence offered by the prosecution is not granted, the defendant may offer evidence without first having reserved that right.