The Anniversary Man by R.J. Ellory
The serial killer to end all serial killers is out there and only one person in the whole city knows it...
Twenty years ago John Costello's life, as he knew it, ended. He and his beautiful girlfriend, Nadia, were victims of the deranged 'Hammer of God' killer who terrorised New Jersey City throughout the summer of 1984. Nadia was killed instantly. John survived, but withdrew from society, emerging only to work as a crime researcher for a major newspaper. Damaged he may be, but no one in New Jersey knows more about serial killers than John Costello.
Then a new spate of murders starts - all seemingly random and unrelated - until John discovers a complex pattern that links them. But could this dark knowledge be about to threaten his life?