- Evidence
- At about 7:50, Conan, Ran, and Kogoro heard Iwama talking loudly to himself about a contact lens he dropped. When Iwama said he found it Conan and Kogoro witnessed Iwama’s shoji screen close.
- At about 8:00, Kogoro and Conan saw a boat with wine pass by their shoji screen. Conan noticed something peculiar about it.
- When Anzai found the body and screamed, Conan, Ran, and Kogoro went out to see what was wrong. Conan noticed Iwama put his jacket on while rushing to the scene.
- Conan deduced, by the angle Kaneda’s body was positioned, that Kaneda faced the murderer when standing at the foot of the table. The murderer then stabbed Kaneda and Kaneda fell on top of the table.
- Room #8 was completely dry, meaning the murderer did not swim in the waterway before entering the room.
- Conan noticed a black substance on Kaneda’s thumb which had a peculiar scent.
- Anzai saw Kaneda going to room #8 before he was murdered. When she asked him about it, he told her he had an appointment with someone there.
- The other guests only saw boats, not people, on the waterway.
- The door to the boat storage is always locked and Anzai is the only one with keys to enter it.
- Conan found that the big boat had the same black substance that was on Kaneda’s thumb. He asked Anzai if this was the boat which had whiskey and the ice from before and she confirmed it was. She also said this boat was scheduled in advance to bring food at 7:30 and whiskey at 8:00 to room #3 which was where the party was supposed to be. Conan looked under the floor panels of the boat and saw it was spacious inside.
- Conan checked room #3 and found two suspicious things. One was that only one pair of chopsticks had its wrapper. The second was a small hole and wet stain at the corner of room #3’s shoji screen sill.
- Not revisited by Conan but still a clue – When Iwama first appeared, the chefs said that Iwama bought lots of food regularly, even if he did not finish.
Kogoro via Conan, described how the murderer entered room #8 using the big boat on the waterway. The big boat had enough space in it to hide someone with small body. First, the murderer asked that all the food to room #3 be delivered on the big boat. After removing the food, he took off the wooden boards and got in the boat. Using the sensor, the boat was en route to return to the place where the boats are parked. On the way there, the murderer used his foot to turn off the switch for the sensor. The boat’s motor stopped and he arrived at room #8, where Kaneda was waiting because the murderer requested to meet in private. Kaneda must have been surprised but probably did not suspect this person would harm him because this person was a close friend. The murderer then stabbed Kaneda and positioned his body facing the corridor to appear as if the he had not used the waterway.
The murderer got back into his boat, flipped the switch to turn the sensor back on and the ship returned to the spot where all the ships were parked. The murderer was able to return to his room because the boat was scheduled to deliver whiskey to room #3 at 8:00. During this trip, with the murderer still inside the boat, the boat passed by Conan’s open shoji screen. Conan noticed that the waterline was high, meaning the boat was deep in the water despite only carrying the whiskey set, which proves the murderer was inside the boat.
Inspector Megure realized that to do all of this, the murderer would have to be in room #3 by himself and be a close friend to Kaneda. He figured Nobuo Iwama is the murderer which Conan agreed with. Conan believed Iwama made Kaneda meet with him in private and sent Arai to buy cigarettes, which Iwama knew was not a brand sold in the restaurant. Iwama reminded them he was looking for his contact lens at the time of the murder. Conan points out Iwama could be carrying a tape recorder but Iwama said it was for business.
Conan then explains how Iwama closed the shoji screen without being present in the room. Iwama used a rubber band, a pin, the wrapper of disposable chopsticks and ice. He tied the rubber band around one pin Iwama attached to the shoji screen left frame and to another pin on the left side of the shoji screen. Next, he wrapped the wrapper on the opposite side of the shoji screen and pinned it against the adjacent shoji screen frame using the pin. He opened the shoji screen up to the wrapper and pinned it in place. So, the rubber band was stretched from the left frame to the left side of the shoji screen, while the right side of the shoji screen was pinned to the left side of the wrapper. The right side of the wrapper was pinned to the right side of the frame. This setup held the shoji screen open by the wrapper, with the rubber band trying but unable to snap back into a relaxed form and shut the door with it. Iwama put a piece of ice from the food in the middle of the wrapper, which, when melting, caused the wrapper to soak up water and tear. Since the wrapper that was holding the door in place was split, the shoji screen had nothing to hold it in place and closed because the rubber band wanted to snap back into its relaxed form.
Conan found no traces of this technique in the room, except for the wet corner of the shoji screen and a small hole. This means Iwama cleaned up the rubber bands and pins, disposed of the tape and tossed the wrapper in the waterway. However, Conan had conclusive evidence which was the sauce for the milt Kaneda ordered. When the boat carrying the food first arrived, Arai spilled some sauce on the boat accidentally. Conan recounts that when Anzai screamed, Iwama came out of his room and the first thing he did was stop to put his jacket on instead of rush to see the scene. Since he might have done this to cover up the milt stain, Iwama was probably in the boat and some sauce spilled on him from the boat’s wooden panels. Iwama showed the police he had a stain on him but said he got it from knocking a plate over while looking for his contacts lens. Conan questions this, and brings to light that Kaneda had some sauce on his thumb, even though he left the room before the food got there. Conan finalizes his deduction by describing that Kaneda grabbed Iwama’s arm as he was being murdered, and that Kaneda’s fingerprint would still be on the stain on Iwama’s shirt. After hearing this, Iwama confessed to killing Kaneda. He reflects that if Kaneda had not ordered the blowfish milt, which was not part of the original reservation, his plan would have been perfect.
Kaneda found out long ago that Iwama used a student’s thesis as his own. Kaneda used this as blackmail to make Iwama recommend him at the professor’s selection meeting. Iwama also prepared up to five million yen to pay Kaneda off but got fed up about the situation and decided to kill him.
