The Drop - Michael Connelly

In his fierce search for a new case, Detective Harry Bosch discovers a killer hiding behind suspicious DNA evidence — and a political conspiracy that could destroy the Los Angeles Police Department.
DNA from a 1989 rape and murder matches a 29-year-old convicted rapist. Was he an eight-year-old killer or has something gone terribly wrong in the new Regional Crime Lab? The latter possibility could compromise all of the lab's DNA cases currently in court.
Then Bosch and his partner are called to a death scene fraught with internal politics. Councilman Irvin Irving's son jumped or was pushed from a window at the Chateau Marmont. Irving, Bosch's longtime nemesis, has demanded that Harry handle the investigation.
Relentlessly pursuing both cases, Bosch makes two chilling discoveries: a killer operating unknown in the city for as many as three decades, and a political conspiracy that goes back into the dark history of the police department.