Just finished an article from my ripped-out pile, from June I think, about something similar -- a Belgian teenager who joined a radical Islamist group in Antwerp and then went to Syria and joined a group that became part of ISIS. His father struggled for years to get him back and finally succeeded, partly because the kid wasn't completely on board at that point anyway and had been beaten and imprisoned by the group because of it. Lots of horrifying details about the group's casual beheadings, shootings, torture, etc. When the kid got back to Belgium he gave information to authorities but they prosecuted him anyway because apparently they don't plea bargain in Belgium. The kid got a light sentence, however, and now he's crazily considering going back to Syria.