Catch Me (Embryo: A Raney & Levine Thriller, Book 4) by J.A. Schneider

A terrifying serial killer who just targets couples, and leaves taunting notes for the NYPD signed CATCH ME… At a loss, police request the help of doctors Jill Raney and David Levine, police friends and detectives on their own. Both have helped when cops’ hands are tied, or in ways that even police forensics never imagined.
But this killer, a sharp shooter, is always a step ahead. He wears gloves and disguises, shoots victim pairs at random with an unregistered gun, and leaves no physical evidence or eyewitnesses. His only weakness: jealousy to hear that David is also a crack shot, and a creepy interest in the couple’s adopted little son, Jesse, almost one year old, dubbed by the media “the miracle baby,” and already showing signs that he is as intuitive as his mother…