The Muttonchop Murderer is the main antagonist in the Treehouse of Horror XV story, "Four Beheadings and a Funeral", a parody of Sherlock Holmes stories. The murderer is wanted for murdering several London prostitutes by stabbing them in the stomach with a fancy knife. He is called the Muttonchop Murderer due to having muttonchops and it is all the prostitutes see when they see him.
Inspector Wiggum (Chief Wiggum) believes a Hindu market owner (Apu) is behind the murders but detectives Eliza Simpson and Dr. Bartley (Lisa & Bart Simpson) take the case. They bring the recent victim's murder weapon to an antiques shop and the dealer (Comic Book Guy) tells them that the knife is part of a set of seven called the Seven Swords of Osiris. The dealer goes into the back room to see who acquired the swords and comes out with one of the swords in his back with the murderer already gone. They learn the swords were bought by Ebenezer Burns (Mr. Burns) and they find him in an opium den (Moe's Tavern). Burns explains that he bought the collection but sold them for opium to "a fat man with sideburns" and points to a man with that description. The man (Homer Simpson) shows his muttonchops and Eliza accuses him of the murders and pursues him. Inspector Wiggum catches him and the murderer is caught... or so everyone thought.
Simpson and Bartley find another prostitute (Selma Bouvier) stabbed and conclude that the Muttonchop Murderer is still at large. The next morning, Homer is sentenced to be hanged in the town square but Eliza stops the hanging and tells the townsfolk that he was innocent and that she smelled a fragrance of eel pie on the blade. Inspector Wiggum refuses to believe her but the constables (Lou and Eddie) expose his muttonchops concluding that he is the murderer. He explains that he did what he did because he wanted to give Eliza Simpson a case that she couldn't solve and he runs off, and steals a hot air balloon to escape. Just then, Kang and Kodos appear in their colonial spaceship, deflate the balloon and Wiggum blows away in the distance. It is unclear if he survived or not but the next scene show Wiggum and his son Ralph in one of Ralph's dreams flying away on a magic carpet.