The Leavenworth Case by Anna Katharine Green

Horatio Leavenworth is a New York merchant whose material wealth is matched by his eminence in the community and reputation for good works. He is also the guardian of two striking nieces who share his Fifth Avenue mansion. Mary, her uncle's favorite, is to inherit his fortune at his death. As this mystery opens, that lamentable event has just occurred. Leavenworth has been shot to death and circumstances point to one of his young wards...