The FBI believes the murder of a missing high school student is linked to a child pornography operation, sources tell ABC News. Investigators are seeking Facebook conversations and emails between 16-year-old Phylicia Barnes of North Carolina and four Baltimore men, according to court documents. Investigators have "reason to believe" the communications will uncover evidence of child sex crimes or child pornography, according to an FBI agent. Barnes was missing for four months before her nude body was found in Maryland, about 35 miles from Baltimore. Barnes disappeared while visiting her sister. Her last Facebook message said she was with her sister's boyfriend.