murdered Oshiro in order to avenge the death of his wife. Mrs. Nagai was hospitalized due to a serious sickness, but Tokujiro's earnings were too modest to afford her treatments, so he was forced to borrow money from Kuromaru Finance. Oshiro, whenever he came by to check on the investment, callously bullied Nagai, which the old man endured for his wife's sake. But then Oshiro decided to demand repayment from Mrs. Nagai, heedless of her condition. When she heard that her husband had plunged himself into debt, Mrs. Nagai suffered a breakdown which contributed to her death soon afterwards.
Upon that revelation, Nagai remembers Conan, or rather Shinichi, from an incident ten years ago, when one of a group of children visiting his toy shop had dropped a toy engine to the floor, breaking it. Shinichi found out which child had done it, but Nagai kindly refused to run after the offender for this accident, because he believe the child would come back by himself, which he did.
The startlement from this realization convinces Nagai to turn himself over to the police, and Megure
to conduct a thorough investigation of Kuromaru's dubious business practices. When Megure asks Nagai why he has decided to surrender himself, Nagai replies that a "mysterious boy who has remained unchanged
for ten years" has influenced him into doing so, believing him to be a sort of messenger from his late wife to remind him that he had once had faith in the boy who broke a toy to take responsibility and therefore he should take responsibility himself.