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When Bart was wrongly accused of a prank and was taken to youth court, Grampa revealed that he knew Janet Reno from years ago and that they played chess through the post. Grampa then gave her a call to be the judge for the trial.
Janet Reno heard the testimonies of everyone involved and then got everyone who disliked Bart to stand trial, including Moe for Bart's prank calls to him. Eventually, Fruit Bat Man brought Willie in who confessed it was him, leaving Janet Reno to announce that Bart was found not guilty.
 Behind the Laughter