Last One Out by Jim Crigler

The nicest people live in the suburbs. \ The nicest people commit murder. When nurse Marlene Saur is poisoned in the offices of the orthopedic practice she works in, suspicion naturally falls on the last person to see her alive, her ex-husband, Ed Penfield. Detective John Mason has to walk a very fine line between Ed and his estranged brother (and Mason's own friend), Ron Penfield. But it is Mason's job to follow the evidence where it leads, without regard for his friendship with Ron, and the available evidence points directly to Ed.