Every Dead Thing by John Connolly

Tormented and racked with guilt over the brutal slaying of his wife and daughter, Charlie Parker, ex-cop with the NYPD, agrees to track down a missing girl.  It is a search that will lead him into an abyss of evil.  At the same time, he gets warned by an old woman that 'The Travelling Man' is about to strike again.  Multiple strands converge with a horrific confrontation in which hunter and hunted are intimately connected by guilt.