1x682 - Detective Conan

After discussing the suicide cases with Sato, Conan concludes that Takagi was looking for his mentor's girlfriend who never got news about his death. She committed suicide believing Date left her. The police find the girlfriend's old English teacher who mixed up the two Watarus and blamed Takagi for her death. Before Sato can get any information about Takagi's whereabouts, the old man succumbs to the poison wine he was drinking.