Samaritan by Richard Price

Then, disaster: he is found beaten nearly to death in his own apartment. He knows who did it, but he's not talking, and he refuses to press charges.
It is up to Detective Nerese Ammons-a childhood acquaintance from the projects-to get Ray to tell her what happened.
Alternating between investigations of the people in Ray's life most likely to do him harm and listening to his fevered ramblings about their shared past as he slips in and out of consciousness, Nerese is charged not only with uncovering the perpetrator of this assault but with understanding what kind of victim is more afraid of the truth than of his potential murderer.
Samaritan is an electrifying story of crime and punishment, of character and place, of children and their keepers - a novel of literary suspense that explores what happens when, caught up in the drama of one's own generosity, too little is given, too little is understood and the results threaten to prove both tragic and deadly.