Yukie couldn’t kill him directly because she needed an alibi. So she tricked him. On the day of his disappearance, she asked him to meet her at the abandoned shrine at 7:30 PM, claiming she had discovered something important about his past. She gave him a bottle of water laced with sleeping pills. He drank it on the way, feeling drowsy.
Conan then looks into the locket. He asks Ran to investigate Yukie’s past. Ran discovers that Yukie had a younger sister named who died in a car accident ten years ago. In the accident, a drunk driver hit their car. The drunk driver? A young, promising architect named Keisuke Sonoda. Detective Conan Episode 406
He explains: Ten years ago, Keisuke Sonoda caused an accident that killed Miyuki, Yukie’s sister. Keisuke was never criminally charged due to a lack of evidence that he was driving, but civilly, he paid a large settlement. He later met Yukie, who apparently did not know his connection to her sister’s death. They married. Yukie couldn’t kill him directly because she needed
Yukie discovered the truth about the locket one year ago. She found the old photo and recognized her sister. She realized her husband was the man who killed her sister. She pretended not to know, but she began planning her revenge. She gave him a bottle of water laced with sleeping pills
Kogoro, excited by the prospect of a high-paying case, immediately puts on his serious face and invites her in.
Initially, it looks like an accident or suicide. But Conan notices the critical contradiction: Keisuke’s watch is broken, showing the time of 2:15 PM, and the date on the watch is the day he disappeared. However, the pathologist later confirms that the time of death was around 8:00 PM that evening. If he fell at 2:15 PM, he couldn’t have died at 8:00 PM. Therefore, the watch was smashed deliberately to mislead investigators.