Guns and pool parties: Secrets of an IS smartphone Mobeen Azhar An estimated 900 people left Britain to join IS and similar groups. The group calling itself Islamic State was responsible for around 14,000 deaths. And today, many British IS fighters remain unaccounted for. In the aftermath of IS's war in Syria, Louise Callaghan, Middle East correspondent for The Sunday Times - working with a local translator - got hold of a hard drive containing files from a smartphone. BBC/Mentorn Media Journalist Mobeen Azhar investigates what made these young men join ISIS and what happened to them. The stills, video footage and screen grabs - which can be seen in a new BBC documentary - show the lives of British men who left their homes and crossed continents to fight.