Mr. Monk and the Class Reunion - S5-E6
Factual error: Stottlemeyer says that if Diane killed herself, her suicide note would go on the public record (and her old nurse would recognize it as a copy of her decades-old note). Since when are suicide notes made public?
Answer: Notice also that in the opening credits scene when he is touching parking meters her also wipes his hand on his clothes each time he does it.