A Darkness More Than Night by Michael Connelly

From the publisher (source: The Internet Book List):
From the publisher
The novel begins when McCaleb, an FBI profiler forced into retirement following a successful heart transplant, agrees to lend his expertise to a particularly baffling murder investigation. The victim is Edward Gunn, an alcoholic lowlife with a violent past. He was once arrested -- by Harry Bosch -- for the murder of a Los Angeles prostitute but managed, despite Harry's best efforts, to avoid prosecution. McCaleb's analysis of the crime scene reveals a number of anomalies: an unexplained head wound, a phrase ("Beware, beware, God sees") written in medieval Latin, the replica of an owl placed in the vicinity of the corpse. Following his instincts, McCaleb locates mirror images of these arcane clues in a number of paintings by Harry's namesake, the 15th-century Dutch master, Hieronymous Bosch.

Harry, meanwhile, is serving as chief investigator and star witness in the sensational murder trial of a world-famous Hollywood director, and has no idea that he's just become the primary suspect in an unrelated investigation. As the trial progresses, it becomes increasingly clear that Harry's testimony is critically important and that any attempt to destroy his credibility will undermine the case against a vicious, well-connected killer.

Eventually, Harry learns about McCaleb's suspicions and forces a confrontation. McCaleb takes a second look at the accumulated evidence and begins to discern the outlines of a very different scenario.

This book is part of the "Harry Bosch" series.
Here are some other books from this series: