Gone for Good by Harlan Coben
From Goodreads: As a boy, Will Klein had a hero: his older brother, Ken. Then, on a warm suburban night in the Kleins’ affluent New Jersey neighborhood, a young woman — a girl Will had once loved — was found brutally murdered in her family’s basement. The prime suspect: Ken Klein. With the evidence against him overwhelming, Ken simply vanished. And when his shattered family never heard from Ken again, they were sure he was gone for good.
Now eleven years have passed. Will has found proof that Ken is alive. And this is just the first in a series of stunning revelations as Will is forced to confront startling truths about his brother, and even himself. As a violent mystery unwinds around him, Will knows he must press his search all the way to the end. Because the most powerful surprises are yet to come.