says yeah,ives ive was a fighte. >> the detainees are questioned and marched off to prison. one guy stood out, a 34-year-old american from sugarland, texas. warren christopher clark comes from a military family. but the muslim convert was a substitute teacher before coming to isis territory. he claims he just sold candy to support himself with isis and spent a lot of time reading. >> i would say most people, yeah, they wanted to go fight or work in some area. i wanted to actually go see what the group was about and what they were doing. >> reporter: his words rang a little hollow. how could he not have known? in online videos the group proclaimed its fanatical view of islam and documented the brutal violence it inflicted on people.