Amagi and Bando were murdered by
Toyoko Kanemitsu, but under a more indirect motive. Kanemitsu, a passionate mystery fan, had written a book titled
The Melting Weapon and submitted it under the pen name "Yamiyo Dorosue" to the publishing company where Chino worked as a reviewer and censor. However, Chino judged the script as being too awful for publishing, and he openly voiced his derision of the author's writing skills and her pen name while visiting Kanemitsu's café, without knowing that he was addressing the very subject of his criticism. Thereupon Kanemitsu decided to take revenge on Chino by framing him for the murders of Tatsuya Amagi, since he was already hated by most of his neighbors, and Hikoichi Bando because he had been too negligent in challenging Amagi for his disorderly conduct.
Conan's clue for discovering Kanemitsu's guilt were the mystery books she had brought to her café and removed after the murders; all of them featured short stories she had already successfully published, and Agatha Christie's The ABC Murders, on which the case was incidentally patterned based on the victims' last names and Kanemitsu's pen name. Kanemitsu, admitting her guilt, subtly left those clues so that only a true mystery fan, who would be Conan, would be able to expose her as the culprit.
In the episode's post-credit scene, a short review of
The Melting Weapon is provided, demonstrating that Chino's assessment actually had a solid basis in fact. Kanemitsu had proposed a highly unrealistic murder method using a poisoned-covered slug as a weapon. While the victim was asleep, the murderer would release the slug into his bedroom. When the slug ended up on the victim's face, the poison would seep through the skin into his bloodstream, killing him, and the salty sweat exuded by the victim's death throes would melt the slug away, leaving no murder weapon.