S1·E653 The Design of Poison and Illusion (S)

The police arrive and their investigations reveal the baumkuchen was cut evenly into eight pieces and that only one of the piece was poisoned. As police interviews the suspects while the widow, Serika Wakamatsu, is excluded since she was never close to the baumkuchen tray. Meanwhile, the police detectives in Nagano reveal to Heiji that Wakamatsu's killer reorganized the bathroom tiles to hide the dying message; The tiles used the crazy diamonds optical illusion giving the impression that it could not be rearranged without breaking the pattern. When arranged back to normal, the message reads "SON" indicating Ikuro was Wakamatsu's killer.