Case Closed: Season 1, Episode 320

1 - 320: Ninja Art: The Art of Alibi Construction

Yuuichi Kusaka, a client of Kogoro's, is found dead in the park. Conan then sets up a meeting at Kogoro's office where the police and two suspects are gathered. After knocking Kogoro out with a tranquilizing and using his voice changing bow-tie to impersonate Kogoro, Conan reveals the culprit.