Butcher's Hill by Laura Lippman

PI-for-hire Tess Monaghan is hired by ex-felon vigilante Luther Beale. He is recently out of prison and wants to make amends to the children who witnessed his crime (which he says he doesn't think he committed by the way). It isn't such a hard job but as time goes on, witnesses keep dying. Tess is confounded by the trail of lies, deception and murders. The third in a series of Tess Monaghan novels, the reader is surprised by the unveiled events which made for a good read. Would recommend to you mystery buffs. Sandy Penton