Back at the Barnyard (2007)

Season 2: Episode 45

Otis and his friends become cops after another cop gets injured, and they try to solve a crime that is about stealing in a donut store. They find the suspects are Mrs. Beady, Snotty Boy and the Farmer. They try to interrogate them, but they're all innocent. They then learn that Pig is the real thief because he wore a burglar costume every time he goes to get donuts for his friends.