In this Best of Nancy Grace episode ....The murder of Sister Cathy Cesnick in 1969 is still an intriguing and unsolved mystery after almost a half century. The 26-year-old was a teacher at Archbishop Keough High School when she disappeared. Did this Catholic nun know too much about dark secrets of sexual abuse of students?Nancy Grace explores the “The Keepers” mystery in this Crime Stories episode, along with Gemma Hoskins — known as “Grandma Nancy Drew” for her determination to find answers in this case, private investigator Shane Waters, New York psychologist Cary Stark, and Crime Stories contributing reporter John Lemley.