h.s.i. >> this team is tirelessly working to try to identify the worst of the worst pedophiles. >> using photos,lxx h.s.i. trac her to a suburban philadelphia home. >> for example, going into wawa, she was walking across to the refrigeratorment i worry every single day that something is going to happen. i do. >> nationally, since 2003, h.s.i. has opened more than 31,000 investigations into child exploitation resulting in 8,000 criminal indictments. >> the advent of technology, while it's largely used for good and legitimate purposes, presents its challenges in law enforcement in how we try to track down predators and how they can hurt children. >> according to the national center for exploited and missing children, 76% are victimized before they hit puberty. 10% of those are infants and toddlers. puberty. overall, 7 out of 10 child sex abuse victims know their predator. a family friend, coach or a parent. >> we spent a week with the dedicated unit at h.s.i. in our exclusive special protectin