A bottle of carbonated water was evidence in the trial of Ryunosuke Naruhodo for the murder of John Wilson.
The true murder weapon[]
- Main article: The Adventure of the Great Departure
Wilson arranged a lunch meeting with one of his students, Jezaille Brett, at the restaurant La Carneval on November 22. Due to an appointment for a tooth extraction at 1 p.m. that day, the lunch was set to 2 p.m., and only Brett would order food. Unbeknownst to Wilson, Brett would use this opportunity to assassinate him without leaving a trace, using curare. This toxin was unknown to investigators in Japan at the time, and was the subject of one of her research reports.
Head waiter Satoru Hosonaga served the table with one plate of steak and a bottle of carbonated water. Brett laced the water with the poison; although both of them drank from it, the poison would only work if it entered through a wound, so only Wilson, who had undergone a tooth extraction, succumbed. Later, Hosonaga, in reality a chief inspector of Japan's Imperial Police Bureau, heard a gunshot and rushed to the dining area to find Wilson dead and a man nearby. The man, Ryunosuke Naruhodo, was holding a gun, so Hosonaga apprehended him and locked him in a small pantry near the kitchen. During the ensuing police investigation, three photographic prints were taken, including a photo of the crime scene that included the steak plate and water bottle. Afterward, Hosonaga took it upon himself to retrieve the steak plate and water bottle, as well as a second steak plate served to Iyesa Nosa, to preserve them as evidence. A postmortem examination of Wilson's body concluded that he had been killed by a gunshot to the chest.
Brett was eventually called as a witness during Naruhodo's trial. Naruhodo learned of the burn mark on Wilson's wrist, and used it to prove that Wilson had already died when being shot. Brett challenged him to provide an alternate cause of death from the postmortem report, and commented on the inferior forensic techniques used in Japan. This touched a nerve with Hosonaga, who submitted the carbonated water bottle into evidence. Naruhodo accused Brett of poisoning the water.
Although no poison was detected on the bottle, Susato Mikotoba managed to retrieve Brett's research report on curare. In an attempt to "disprove" Naruhodo's accusation, Brett drank the remaining water in the bottle, knowing that it would not harm her. However, Mikotoba's translation notes on Brett's report revealed that the poison would have only affected Wilson, as only he had an open wound in his mouth from the tooth extraction procedure. In response to this, Brett dropped the bottle onto the floor, smashing it into pieces, while the remaining water was absorbed into the carpet. Later, when Naruhodo went to request that Hosonaga bring out the steak plate from Wilson's table, the latter seemed lost in thought, presumably about the smashed bottle.