Triple Cross by James Patterson

Detective Alex Cross hunts down a serial killer who’s murdering entire families—and who will next be coming for Cross.

A methodical killer is targeting multigenerational families in and around Washington, DC—striking under cover of darkness, triggering no alarms, leaving no physical evidence of any kind.  
 
Alex isn’t the only one investigating. Also on the case is a charismatic true-crime author who sees patterns the detectives miss.
 
The writer calls “The Family Man” a perfect crime story. Alex knows there is no perfect crime—the investigation should never become the story. Unless the ending falls somewhere between fact and fiction.