Can I Hire a P.I. to Investigate My Sister-in-Law's Awful Boyfriend?

The author responds to a query submitted by a reader who wishes to hire a private investigator to look into what the sender perceives as a case of domestic violence. He urges the reader to strike a sympathetic conversation with the family member affected by the relationship. He also considers the possibility of initiating a legal case that will compel the police to investigate without the cooperation of the family member.