Detective Conan S01 E682 The Life-Threatening Broadcast of Love (Crisis State)

"One truth prevails."

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.