The recent attack in Russia by the ISIS-Khorasan and the killing of 150 Russians has sparked international eyeballs. The act is condemned by the international community. Different views have been expressed about this attack and its political implications. In this article, the authors talk about the responsibility of non-state actors in international law and throw light on one kind of such actor called Foreign Terrorist Fighters who have played an integral role for organizations like ISIS-Khorasan. In simple terms, non-state actors are an umbrella concept that encompasses all those actors in international relations that are not States. It comprises individuals as well as entities, the latter spanning a large range of organizations and institutions on the global, regional, sub-regional as well as local levels.