The Girl from Devil's Lake by Judith Jance

Sheriff Joanna Brady is looking forward to the holidays with her busy family and to celebrating her daughter Jenny's graduation from the police academy. But the family is interrupted when a body is discovered beneath a flooded bridge in the Arizona desert and Joanna is called on to the case. A young boy was murdered, and the details of the crime scene tell Joanna two things: This was not the killer's first murder. And it's only a matter of time before he kills again. As Joanna digs deeper into the case, she begins to understand this murder is just one piece of a much, much bigger puzzle. She uncovers unlikely connections between cases of mysterious deaths and missing persons, long since gone cold, that extend far beyond the confines of her small town and include the discovery of a body near Devil's Lake, North Dakota.