Kazuyuki Kawai invites Kogoro, Ran, and Conan to his houseboat for dinner and to view the fireworks. During the fireworks, Kawai's guest, Tsuneo Yamasaki, is found dead from electrocution.
Murder
Location:Unabara Boat
Victim:Tsuneo Yamasaki
Cause of death:Electrocution
Suspects:Sayori Unabara, Fukuo Unabara, and Kazuyuki Kawai
Kogoro deduces that Tsuneo slipped on some water causing his fishing rod to touch exposted electrical wiring causing his death. Conan investigates and realizes its a murder.
After tranquilizing Kogoro, he reveals the culprit, Kazuyuki Kawai. He tells that when he and Tsuneo Yamazaki were alone on the deck, while Yamazaki wasn't looking, he attached the cutter knife-edge. Then, he attached the hook on the hull, he pretended that a fish was pulling on the rod asking Yamazaki for help, he had Yamazaki grab onto his fishing rod, and used the cutter knife-edge to cut the line. He made the fishing rod to touch the electric wire, causing Yamazaki to fall, and if he was bare handed and bare footed like Yamazaki. Then he ask to show what's inside in his pocket and it was skin colored rubber gloves and saying he is using those for fishing seems pretty usual. But then Yamazaki's death wasn't an accident but he had the urge to kill. He then said "Just think about it." If he pulled the fishing line from the side of the boat, the fishing line would've been pulled vertically, if the line gets cut from the side of the boat, he should vertically. But, in order for the fishing rod to touch the electric wire from the side of the boat, it would have to fall parallel. In other words, as soon as the fishing line was cut, he pushed Yamazaki in a parallel direction. By doing this, the fishing rod made contact with the electric wire. He had the intention to kill. But Kazuyuki was telling that he's not the culprit and asking solid evidence but Kogoro hold the solid evidence, it was his lighter but it won't light up. Then he also said he lit up a cigarette with the lighter before the departure, and asked why he is not using it anymore. Then they saw a piece of vinyl stuck on the lighter's wick, it happened when he was burning the electric wire, he used the lighter to melt the rubber coating leaving the electric wire exposed, after that, he wore his rubber boots on the deck, and the skin colored gloves for electrical insulation, he electrocuted Yamazaki. Then, by keeping a falling pose, he took the boots off and trew them away, hid the rubber gloves in his pocket, and pretended to be unconscious.
Kazuyuki confesses and revealed Tsuneo loaned him money with high interest, and tried to take over his company, that's not all. As the guarantor for this debt, he had to make him the beneficiary of his life insurance with a large payout. If he didn't kill him, he would've been killed eventually.
