Leo was a student at Monk's Junior High School as well as the class bully. He ate one of the cupcakes at the bake sale without paying for it, causing Sherry Judd and Adrian Monk to warn that they will tell on Leo for his actions (with Leo squirting Monk's outfit with chocolate syrup). Principal Thicket, witnessing this debacle, took him to the Principal's office, and gave him several weeks of detention. Leo then claimed he won't steal again (although he then took Monk's clarinet to show he wasn't serious as well as make an unsubtle threat to the both of them), his only giving it back when Jimmy Wagner told him to. Secretly, however, he stole Sherry's lock for her locker and replaced it with his own as a plot of revenge for her and Monk "squealing" on him. He then sneaked into the cafeteria and placed the lunchbox containing the bake sale money inside one of the bake sale boxes and left for Sherry's locker. He then placed the lunchbox inside and replaced his lock with her lock, thus framing her with stealing the lunch money. He made two mistakes, however: First, he forgot to set Sherry's lock back to zero, which she usually did (although no one except Monk would notice this). Second, while stealing the box that contained the lunchbox, he left his fingerprints on it (or more accurately, the blue frosting from the cupcake he ate earlier all over the side of the box). When Monk confronted Leo about this, he told him that he knows he did it, though not how. Leo, confident that Monk won't find out how, nor would he let him, then proceeded to place Monk inside a locker. This proved to be his fatal mistake, as Monk managed to deduce exactly how Leo did it from being inside the locker, although the trauma he suffered from being locked inside forced him to whisper to Sherry that he solved how Leo did it. After Monk explained how Leo stole the box, Thicket, despite Leo's repeated denials that he stole the money, forced him to empty his pockets, producing a wad of cash. Thicket then recognized the money as being from the bake sale (due to one of the five dollar bills containing a "good luck" note written by Thicket himself), and proceeded to drag him to the Principal's office for "a little talk." Exactly what happened to him after that is unknown, although it can be assumed that he got a very severe punishment for his actions.