One of Us (Urban Underground #5)

In the alley on his way home from work, Derrick Shaw witnesses a murder. To save his life, Derrick promises not to reveal the identity of the shooter, a former Tubman student. But he feels sick and guilty about his vow of silence. It would have been easier if Rafe Wexford was a gangbanger, shot dead, but Rafe was a good guy attending City College.