The golem of Paris / Jonathan Kellerman and Jesse Kellerman.

Enhanced descriptions from Syndetics:

From two #1 bestselling masters of crime fiction comes an extraordinary thriller about family, murder, and the secrets that refuse to stay buried.

It's been more than a year since LAPD detective Jacob Lev learned the remarkable truth about his family, and he's not coping well. He's back to drinking, he's not talking to his father, the LAPD Special Projects Department continues to shadow him, and the memory of a woman named Mai haunts him day and night.

And while Jacob has tried to build a bridge to his mother, she remains a stranger to him, imprisoned inside her own tattered mind.

Then he comes across the file for a gruesome unsolved murder that brings the two halves of his life into startling collision.
Finding the killer will take him halfway around the world, to Paris--the city of romance, but also of gritty streets, behind the lights. It's a dangerous search for truth that plunges him into the past.

And for Jacob Lev, there is no place more frightening.

Jonathan Kellerman has long been known for his mastery of criminal psychology and his ability to create thrilling novels of nuanced drama and suspense. But in The Golem of Paris , he and Jesse Kellerman raise that suspense to a whole new level.