S1E654 : The Design of Poison and Illusion (Poison)

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.