Detective Loomes is the 13th omake of the series and was originally published in The 15th Log: "Thriller Bark" on February 4, 2011. It was made up as a response to a question asking what if Luffy and his crew are detectives. In this omake all the characters' names are parodies based on well known people and well known fictional characters.
The story begins with Detective Sherlock Loomes pointing at Cholyde, accusing him of being guilty. Cholyde insists that it is not him, so Loomes accuses Namiron who also claims that it is not her. As Loomes accuse Nakamura, Doctor Usotson hit him telling Loomes to stop relying on his instinct. Loomes complains it hurt, and Usotson tell him that if the suspect is guilty, then would he just admit to it so easily? Loomes then gives up saying that this case is unsolved, which at that Usotson again hit him for giving up so easily. Loomes wants to go on a stakeout, with donuts and coffee, but Usotson says they do not have to go on a stakeout, as a murder happened in a closed room, and the guilty person is someone in this room.
He then goes over the facts they already know; the murder happened in the room at 3 o'clock. Namiron, who works in this mansion, was walking past the room when she heard a scream. In a hurry, she opened the door, but Bronegie was already decreased and the floor was covered in blood. The room was completely closed, with no windows and the only exit or entrance was the door but it was locked. The victim, Mister Bronegie, a very rich man, seems to have suffered a blow to the head from a blunt object, which appears to be the cause of the death. He always carried a bag full of cash, but it was missing when he was discovered to be dead, which make this likely to be a robbery homicide. At the time of the death, there were five visitors and a maid at the mansion.
Loomes then has an interview with the visitors and the maid. Namiron, the maid, informs Loomes that she killed people in other towns for money before and Bronegie was annoying, always asking her for her panties. But she insists she's not the killer. Nakamura Hanzorou is next, saying that he loves to slice up passengers on the street, but he claims he did not kill Bronegie. Cholyde says he killed about fourteen people, and he's annoyed at the society, but aren't they all? Robie asks if Bronegie died from being hit with a blunt object. She then says that Cholyde and her specialty is to kill by smashing the butt of their guns but it is not them who murdered Bronegie. Golco Sanjeen says that he killed about thirty people and he wants money, but he's a pro. He only take money from his clients, so it is not him. Frack the Ripper do not remembers how many people he killed as he always wants to slice people up but it is not him.
Loomes says in shock that they all are terrible, every single of them, when Bronegie suddenly come in the room, apologizing for Loomes's trouble and that he thought he was dead, but come to think of it, he's already dead. He also says that he lost his money and slipped and fell on his head in his room. Loomes then points at him, saying that he's the one guilty. Usotson then let all of the murderers leave, apologizing for doubting them to which the murderers say that next time Loomes and Usotson doubt them, they'll kill them.
- Detective Sherlock Loomes: The detective solving the case of who killed Mr. Bronegie. He is based off fictional super-sleuth Sherlock Holmes, and played by Luffy.
- Doctor Usotson: Detective Loomes' pragmatic assistant. He is based off Holmes' assistant Doctor Watson and played by Usopp.
- Bronegie: The very rich, "deceased" man. He is based off real-life industrialist Andrew Carnegie and played by Brook.
- Namiron Stone: The maid at the mansion. She has experience in murder and has killed people in other towns before for money. She is based off Sharon Stone's character, Catherine Tramell, in Basic Instinct. She is played by Nami.
- Nakamura Hanzoro: A street slasher who loves to slice up pedestrians in the street. He is based off real-life samurai Nakamura Hanjirō and is played by Zoro.
- Robie: A mass murderer who specializes in killing by smacking people with the butt of the gun. Her partner is Cholyde. She is based on real-life outlaw Bonnie Parker and played by Nico Robin.
- Cholyde: A mass murderer who has killed about 14 people and is "annoyed at society". He is the second half of the Robie and Cholyde duo. He is based on Bonnie's partner-in-crime Clyde Barrow and played by Chopper.
- Golco Sanjeen: An assassin who has killed about 30 people. He is based off the titular character of Golgo 13, and played by Sanji. The pun here is that "sanju" means "thirty" in japanese.
- Frack the Ripper: A crazy murderer who has lost count of how many he has killed and always wants to slice people up. He is based on the real-life unidentified serial killer Jack the Ripper and played by Franky.
- Even though the log this Omake is at is in the Thriller Bark Arc, the Straw Hats are being drawn according to their designs after the 2 year timeskip.