Past Imperfect — Margaret Maron

The fatal shooting of off-duty detective Michael Cluett, recently transferred from Manhattan to Brooklyn and days short of his 40-year tenure, sets off the series of intertwining investigations. After the shooting, lieutenant Sigrid Harald, Cluett's boss in Manhattan, learns that he and her own boss had worked with her father, also a policeman, and may have shared a dark secret about his death in the line of duty many years before. The subsequent killing of the computer operator checking on the Cluett murder weapon suggests police involvement and leads Harald to probe her father's death.