Defending Jacob by William Landay

Assistant D.A., Andy Barber, is shocked when a boy in his son's eight grade class is found stabbed in a park near the school.  He is certain that an identified local sexual predator is responsible.  As the facts begin to point in a different direction, his son Jacob becomes a likely suspect.  The search for the truth reveals how little truth each family member knows about each other and how little any parent may know about any child.  The author deftly weaves the record of Andy being questioned in court within the larger story. And the ending is a "killer" - pardon the pun.