1x304 - Case Closed (Detective Conan)

Sato reminisces about the bomber case three years ago. Three years ago, a bomber sent a fax to the Tokyo Metropolitan Police containing the location of a bomb in the form of a riddle. Matsuda discovers the bombs location and realizes that the bomb contains a clue an even larger bomb and that the clue is only revealed during the last three seconds before detonation; Matsuda sacrifices his life and allowed the police to locate the second bomb.