When questioned by the investigating detectives, Kyoko claimed to have been out golfing with friends at the time of her husband's death, with their accounts and the evidence in the Shibata house seemingly confirming Kyoko's alibi. As a result, the police suspected Shizuka as Shiro's killer, as he was holding the photograph she wanted to retrieve from him at the time of his death. But ultimately, Conan deduced the truth: Kyoko had in fact murdered her husband.
Before leaving for her golfing trip with her friends, the evil Kyoko waited until Shiro was eating a late night meal before luring him into the entranceway hall, where she struck him in the head with a bokken sword. Kyoko then left for her golfing trip, setting a time videocassette to record Shiro's favorite show as part of her plan to establish an alibi and throw off Shiro's time of death. When she returned home at 7:00 P.M., Kyoko placed the morning's newspaper by Shiro's half-finished meal to make it appear that he had been attacked and killed while eating breakfast. When Kyoko heard Takezo's phone message for Shiro telling him he was coming to get him for their game of mahjong, Kyoko left the apartment and hid in the stairwell so it would seem she hadn't returned home until after Shiro was murdered.
After knocking out Kogoro, Conan impersonated him to reveal Kyoko's scheme, with the final piece of evidence also explaining why it appeared Shiro was holding Shizuka's photograph when he was killed: Kyoko had actually placed it in his hand to hide his true dying message, which was his blood-covered wedding ring; meant to signify he had been killed by his wife. Kyoko was officially exposed when Conan deduced that she was still holding on to her husband's ring, with Kyoko dropping the ring to the floor to show she was. Kyoko then confessed to killing Shiro, and explained her motive: he had become addicted to gambling on mahjong games with Takezo, with his addiction driving them into deep debt. Shiro was then forced to sell many of his and Kyoko's possessions to cover his debts, with Kyoko finally being driven to kill him when he informed her he would be selling her golf clubs and her father's dowry.
When Inspector Sango Yokomizo informed Kyoko they had to bring her into the station, Kyoko went into another room to change before they left. But as she did, Conan realized that she actually intended to commit suicide, with him and the rest of the investigators bursting into the room to find her wielding a katana sword. As she prepared to kill herself, Kyoko ordered everyone to stay back and continued to claim that killing her husband was the only choice she had. Shizuka then approached Kyoko and, after the villainess swung her sword maniacally at her, disarmed her using a hand fan. Shizuka then lambasted Kyoko for wanting to take her own life after killing Shiro, stating that it made her no better than a cold-blooded murderer and advising her to learn to appreciate the value of life before she was taken into custody for her husband's murder.
- Youko Matsuoka also voiced the evil Maya Tachibana, a villainess from Case Closed's first season.