Black Hornet — James Sallis

With this flashback novel to Lew Griffin's past, James Sallis takes readers to 1960s New Orleans, a sun-baked city of Black Panthers and other separatists.
 
A sniper has fatally shot five people. When the sixth victim is killed, Lew Griffin is standing beside her. Though they are virtual strangers, it is left to Griffin to avenge her death, or at least to try and make some sense of it. His unlikely allies include a crusading journalist, a longtime supplier of mercenary arms and troops, and a bail bondsman.