The Clue of the New Pin

Jesse Trasmere is a miser with a deep distrust of the bank. He has made a fortune in China, but keeps it hoarded in his prison-like house. Although his nephew, Rex Lander, receives a generous allowance from his uncle, it is not enough for his extravagant lifestyle. One day Trasmere breaks with routine and informs his valet, Walters, that he is going out of town for a while to avoid an acquaintance from his past. So how does this explain Trasmere's body later found in a locked vault?