Ukraine has identified almost 16,000 names of people lost in a gulag of 180 prisons in Russian-held Ukraine and in Russia itself, as far away as Siberia. It is a war crime to take civilians hostage during a conflict, but that has not deterred Vladimir Putin's regime, and there is evidence they are being tortured, sexually abused and killed in custody. Sky's international affairs editor Dominic Waghorn reports. SUBSCRIBE to our YouTube channel for more videos: http://www.youtube.com/skynews