The thesis explores the protective capacity of International Human Rights Law (IHRL) vis-à-vis victims of disappearances committed by organised criminal groups (OCG), and their relatives. By combining doctrinal legal research with qualitative research on the particular situation of disappearances in the context of the so-called 'war on drugs' in Mexico and the experiences of human rights practitioners engaged with this topic. The research departs from the issue of non-state actors as perpetrators of human rights violations in international law, specifically disappearances, and the question of how state responsibility for such acts can be determined. By focusing specifically on OCG as a non-state actor, this research adds not just to scholarship on non-state actors and disappearances more generally, but also to incipient international legal scholarship on the issue of organised crime and international law. Moreover, the combination of two disciplinary lenses can contribute to discussions around methodology in human rights research. Finally, the thesis provides insight into the complexity of the ongoing crisis of disappearances in Mexico.