For many years both supporters and critics of private military and security contractors have agreed that PMC legal status is ambiguous. As they are neither regular military forces or classic mercenaries it has often been unclear whether, and, how laws, especially international humanitarian law (IHL), can be used to prosecute them, if they do something wrong.
The international laws that exist, such as the Geneva Conventions, or the International Convention against the Recruitment, Use, Financing and Training of Mercenaries, and regional conventions, were formulated with classic mercenaries in mind. Thus, they are generally viewed as inapplicable for use in determining criminal liability.
But a recent paper argues that there is room for hope, Ottavio Quirico argues that, under certain circumstances, private security contractors can be de facto assimilated to subjects formally classified under IHL. In this light, the ambiguous legal status of private security personnel with respect to war should have a limited impact on criminal liability.
His paper is, "War Contexts: The Criminal Responsibility of Private Security Personnel" published earlier this year by the European University Institute in Italy.
His conclusion is:
Overall, the ambiguous status of private contractors under IHL could often be overcome by assimilating de facto their position to that of formally classified parties, In this light, the uncertainty of the official qualification should have a limited impact on criminal liability. The propriety of the current national and international regulation applying to the criminal responsibility of PSC personnel can be questioned from the viewpoint of both equity and completeness. In theory, it affords multiple means for trying PSC personnel responsible for war crimes or direct participation in hostilities. In practice, the unwillingness or incapacity of States to prosecute proves a major obstacle for the efficiency of the system. By overcoming the frame of State sovereignty, the ICC [International Criminal Court] provides appropriate mechanisms for implementing the existing rules, but its jurisdiction is limited by the founding Treaty.