Now that they had caught the culprit red-handed, it was naturally time for the much-anticipated killer's confession. Sure enough, Chiken Kōdai explained her motive. It turned out that this incident had been planned by both her and the gourmet detective Ōkami. Ōkami had somehow learned about the treasure of Twilight Mansion and the secret behind its legend, so he poured all his assets into buying the mansion, hoping to uncover Twilight Mansion's Secret Treasure together with Chiken Kōdai.
Unfortunately, whether due to a lack of brains or bad luck, the two had never found it. To buy the mansion, Ōkami had borrowed quite a bit from the bank. He had originally planned to strike it rich after finding the Secret Treasure and pay the money back, but with the treasure nowhere in sight and the repayment deadline drawing closer, he eventually came up with this plan.
Chiken Kōdai had originally agreed to cooperate with him, but unexpectedly, she turned around and sold him out, using poison smeared on the handle of his cup to kill the unfortunate gourmet detective outright.
Chiken Kōdai had not done it purely for the treasure, either. In fact, her father had once been an outstanding archaeologist. Decades ago, Renya Karasuma had invited many people to Twilight Mansion to investigate the rumored Secret Treasure, and Chiken Kōdai's father had been among them.
In the end, no one uncovered the secret, and Renya Karasuma killed them all—well, upon hearing that, Fang Zheng and Conan exchanged a glance.
That sort of killing-to-silence-anyone-at-the-drop-of-a-hat approach was indeed remarkably similar to the Black-Clad Organization's methods.
As for Chiken Kōdai, she had only noticed something strange in her father's letters decades later. After her father went to Renya Karasuma's Twilight Mansion, he had written letters home to assure them he was safe.