States have obligations to protect the right to life, which include obligations to prevent and respond to violations of this right by non-State actors. Yet, there is no clear approach to determining State responsibility for failing to comply with these obligations. One actor that is notably absent from scholarship on State responsibility and non-State actors is organised criminal groups, despite the fact that their activities can infringe the right to life in many ways. This article critically examines current approaches by the European and Inter-American Human Rights Courts for determining State responsibility for a failure to prevent, in light of the current crisis of disappearances in Mexico. It is argued that in cases where the non-State actors are organised criminal groups, their particular nature and their relationship to the State should be taken into account as criteria for assessing the State’s knowledge of risk and the reasonability of measures taken.