International criminal tribunals have developed a number of legal theories designed to hold individuals responsible for their role in collective criminal conduct. These doctrines of criminal participation, known as modes of liability, are the subject of significant scholarly commentary. Yet missing from much of this debate, particularly as regards the International Criminal Court, has been an analysis of how current doctrine on modes of liability responds to the need to hold collective perpetrators criminally responsible for crimes of sexual and gender-based violence (SGBV). Indeed, many writings in this area of the law address perceived shortcomings in the theoretical underpinnings of modes of liability doctrine in the abstract but ignore the application of this doctrine in concreto. As a result, facially neutral writings on modes of liability may in fact be gendered in application, either because they fail to account for the specific characteristics of sexual and gender-based violence or because they are applied in a manner that requires higher thresholds for finding culpability for the commission of SGBV crimes. This article fills the gap between theory and practice, examining past and present doctrine, and suggesting ways in which the treatment of modes of liability by international criminal courts and tribunals can both properly respond to the need for personal culpability and the dangers of collective criminal activity, particularly as regards SGBV crimes.

On September 27, 2016, the Trial Chamber (Chamber) of the International Criminal Court (ICC or tribunal) rendered its judgment in Prosecutor v. Ahmad Al Faqi Al Mahdi, wherein the defendant was convicted of the war crime of intentionally directing attacks on protected cultural objects. It is the ICC's first such conviction and the first time that an accused has entered a guilty plea at the tribunal pursuant to Article 65 of the Rome Statute (Statute). Al Mahdi pled guilty to co-perpetrating attacks on protected objects pursuant to Article 8(2)(e)(iv) of the Statute for his role in the attack on, and destruction of, ten mosques and mausoleums in Timbuktu. The Trial Chamber sentenced him to nine years in prison.

The jurisprudence of the International Criminal Court (ICC) up to the Lubanga judgment showed definite interpretive trends on the modes of principal liability. This article aims first to make a critical assessment of these trends by focusing on methodological and substantive aspects. On the one hand, the practice of having resort to theories derived from Continental legal systems, albeit legitimate, is based on a methodology that raises some concerns as to the selection and (mis)interpretation of such theories. On the other hand, the Court has clearly adopted a wide interpretation of some critical elements in which the different modes of principal liability are grounded. This choice has caused a significant expansion of the scope of principal liability as well as a breach of the principles of legality and of individual criminal responsibility. In our opinion, the underpinning of these interpretations is a flawed understanding of the criteria for distinguishing between principals and accessories.

This perspective has been overturned by the Katanga judgment, on which the second part of this article will focus. This judgment correctly argues that the distinction between perpetrators and accomplices is grounded only on the autonomous or vicarious character of their contribution to the offence. Furthermore, it follows a partly different approach as to both the methodology and the interpretation of the constitutive elements of principal liability. In our view, this approach better fits both the relevant statutory provision and the basic principles of criminal law.

Both the International Criminal Tribunal for the former Yugoslavia (ICTY) and the International Criminal Court (ICC) have struggled to combine vertical and horizontal modes of liability. At the ICTY, the question has primarily arisen within the context of ‘leadership-level’ joint criminal enterprises (JCEs) and how to express their relationship with the relevant physical perpetrators (RPPs) of the crimes. The ICC addressed the issue by combining indirect perpetration with co-perpetration to form a new mode of liability known as indirect co-perpetration. The following article argues that these novel combinations – vertical and horizontal modes of liability – cannot be simply asserted; they must be defended at the level of criminal-law theory. Unfortunately, courts that have applied indirect co-perpetration have generally failed to offer this defence and have simply assumed that modes of liability can be combined at will. In an attempt to offer the needed justification, this article starts with the premise that modes of liability are ‘linking principles’ that link defendants with particular actions, and that combining these underlying linking principles requires a second-order linking principle. The most plausible candidate is the personality principle – a basic principle that recognizes the inherently collective nature of leadership-level groups dedicated to committing international crimes. Like Roxin's theories describing the collective organizations that can be used as a form of indirect perpetration, the personality principle treats the horizontal leadership group as an organization or group agent whose collective nature potentially justifies the attribution of vertical modes of liability to all members of the horizontal group. Although this article does not defend the doctrine of indirect co-perpetration, it does conclude that combined vertical and horizontal modes of liability, whether at the ICTY or ICC, implicitly or covertly rely on something like the personality principle in order to justify collective attribution to the horizontal collective.