The Last Coyote (Harry Bosch #4) by Michael Connelly

Harry attacked his commanding officer and is suspended indefinitely, pending a psychiatric evaluation. At first he resists the LAPD shrink, but finally recognizes that something is troubling him and has for a long time. In 1961, when Harry was twelve, his mother, a prostitute, was brutally murdered, and no one has ever been accused of the crime.

With the spare time a suspension brings, Harry opens up the thirty-year-old file on the case and is irresistibly drawn into a past he has always avoided. It's clear that the case was fumbled and the smell of a cover-up is unmistakable.