Chris Pittman shot his grandparents, Joe and Joy Pittman, at close range and then set their house on fire. According to family members, Chris, a well-mannered and shy 12-year-old, who lived with his grandparents, loved them more than anything. So, why would Chris kill them? Is the anti-depressant, Zoloft, which he was prescribed shortly before the murders, really to blame, as his lawyers claim? Correspondent Erin Moriarty has an exclusive interview with the now 16-year-old and reports for 48 HOURS MYSTERY.