David Zimmerman:  How come I 've never heard of this guy ?
Derek Morgan: Have you ever heard of Efren Saldivar ?
David Zimmerman: No .
Derek Morgan: David Parker Ray ? How about John Edward Robinson ? See , at any given time , we have at least 25 open cases . Every year we 're able to close around _ 15 _ , yet new ones still seem to pop up . There are more serial killers out there than you may think .