The Design of Poison and Illusion (Poison) Meitantei Conan : Season 1 Episode 654

Conan and Heiji resume their investigation while Ran and Kazuha gossip about Shinichi's confession towards Ran. Conan and Heiji discover powdered poison on Ikuro's doorknob and Serika's slippers; the evidence indicates her as Ikuro's murderer. The two confront Serika whom is found dead in her office from cyanide poisoning. Wakamatsu's secretary, Satake Yoshimi, reveals that per Serika's will, a letter of confession to Wakamatsu's murder is to be given to the police upon her death; the letter confirms Ikuro was the murderer and Serika's role in hiding the dying message.