“Complicity in International Law”: An Overview. Book Discussion

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This post is part of our book discussion on Miles Jackson’s “Complicity in International Law“.


No one is ever accused of being complicit in something good. Across areas of law, complicity – the idea of participation in another’s wrong – has received increased attention in the last decade. To take one domestic jurisdiction, England and Wales, accessorial liability in private law and criminal law has been subject to detailed re-evaluation. In international criminal law, the acquittal of Momcilo Perisic by the ICTY Appeals Chamber brought deep recrimination and comment. And in the law of state responsibility, the complicity rule in Article 16 of the Articles on State Responsibility is increasingly invoked in the context of the arms trade, counter-terrorism, and development aid.

This increased attention forms the background to the book. My overarching aim is to understand and analyse how international law regulates individual and state complicity. This overarching aim is supplemented by, where appropriate, critique as to the scope of the relevant rules and a normative claim as to how complicity rules ought to be structured. To this end, the book is structured as follows. Part A builds an analytical framework for understanding complicity rules and defends the normative claim mentioned above. Part B addresses complicity in international criminal law, including complicit omissions and command responsibility. Part C does two things. First, it considers state participation in the wrongdoing of other states and tracks the move from what I call specific complicity rules to the general rule on aid or assistance in Article 16 of the Articles on State Responsibility. Second, it addresses state participation in the actions of non-state actors. In doing so, it appraises the claim that complicity has permeated the secondary rules on the attribution of conduct in international law and proposes a non-state analogue to the rule in Article 16. Part D concludes.

Building an Analytical Framework and Defending a Normative Claim

Before turning to the scope and structure of complicity, it is worth asking why we have complicity rules at all. In the criminal context, the inculpation of those who help or instigate seems to flow naturally from the wrongfulness of the principal act. Likewise, in civil law and the law of state responsibility, where the principal act would be wrongful if committed by the accomplice, it is easy to recognise the force of the International Law Commission’s aphorism: one ‘cannot do by another what [one] cannot do [oneself].’ Outside of these situations – think inducing breach of contract and its comparative analogues in private law – different legal systems and areas of law take different approaches. The varying needs and purposes of the regime inform both the existence and scope of the complicity rule.

Across areas of law, it is helpful to analyse complicity rules in an inter-dependent tripartite framework. This framework – which I construct in Chapter 2 of the book – concerns (a) the forms of complicity prohibited; (b) the nexus or connection required between the accomplice’s act and the principal wrong; and (c) the fault required of the accomplice. In addition, in Chapter 2 I also defend a normative claim as to how complicity rules ought to be structured. Ideally, there should be differentiation in the attribution of responsibility between the accomplice(s) and the principal. This claim is easier to see in the context of criminal law, where the principles of culpability and fair labelling do much of the critical work. For states, an analogous idea of sovereign autonomy (and fair labelling) informs the claim. In the subsequent parts of the book, I use the framework and normative claim to assess international law’s approach to complicity.

Complicity in International Criminal Law

In Chapter 4, I show that that in international criminal law, the following features mark archetypal doctrines of complicity. First, there is breadth in the forms of complicity prohibited – international criminal tribunals have emphasised that any acts of assistance, encouragement, or moral support may be sufficient. Second, this assistance is required to have a substantial effect on the commission of the crime, though the restrictive bite of this requirement does not seem great in practice. Third, the fault element is unstable. On one hand, the Kunarac Trial Chamber’s assertion that the accomplice must ‘take the conscious decision to act in the knowledge that he thereby supports the commission of the crime’ is defensible as a matter of law and principle. On the other, Stewart has convincingly shown that this standard of knowledge has bled into recklessness in practice.

That final point might lead naturally to a discussion of Perisic and specific direction – this is something I address in Chapter 4 (pp. 80-85). For present purposes, it seems unnecessary to revisit it now except to say that some of the underlying anxieties could be better addressed through (i) renewed focus on the other elements of the complicity rule; (ii) the increased use of conditions and monitoring in the provision of assistance; and (iii) an assessment of the possibility of any defences to knowing participation. Instead, it is worth emphasising that the normative claim as to the structure of complicity takes hold here. I argue that in international criminal law, accomplices ought to be liable for their acts of complicity – there ought to be differentiation among participants in the attribution of responsibility.

Concluding the book’s discussion of international criminal law, Chapter 5 considers complicit omissions. As to aiding and abetting by omission, it analyses the key case of Mrksic, and, drawing on the common law, proposes a framework for thinking about the key criterion of a duty to act. As to the doctrine of command responsibility, it argues that one part of the doctrine – knowing failure to prevent the commission of a crime – may be understood as a complicit omission and justified in those terms. Other parts of the doctrine – particular the failure by a commander to punish subordinate crimes – require alternative justification.

State Complicity – Assistance to Other States

The book then shifts, in Chapters 6 and 7, to consider state complicity in the wrongdoing of other states. In the first place, there is a narrative here that matches the historical evolution of complicity rules in other areas of law – that is, the shift from specific rules to a general rule. In respect of the former, in Chapter 7.2 I analyse one example of what I call specific state complicity rules: international law has long prohibited the provision by one state of its territory to another that facilitates an act of aggression against a third state. This rule is specific at the level of the forms of complicity – the provision of territory – and in terms of the principal wrong – aggression. In respect of the latter, it was (partially) these instances of specific complicity that underscored the ILC’s inclusion within the Articles on State Responsibility of what ended up as Article 16 – the general prohibition on aid or assistance in the commission of a wrongful act by another state.

In recent international practice and scholarship, much of the action has concerned the contours of the rule in Article 16. In terms of the tripartite framework of the thesis, Chapter 7.3 shows that it is marked by the following elements. First, the modes of complicity only extend to material aid; instigation or incitement is excluded. Second, the aid must materially facilitate (or significantly contribute) to the principal wrong. Third, the fault element is likewise (relatively) unstable; I argue that the textual standard of knowledge of the circumstances of the wrongful act is (and ought to be) sufficient. And finally, as to the structure of the rule, it is clear that the assisting state is held responsible for its own acts; the acts of the principal state are not imputed to it.

These elements, sketched in bare terms above and addressed in detail in Chapter 7, have been the subject of considerable attention and development, including in Chatham House’s recent report on Aiding and Assisting in Armed Conflict and Counterterrorism. Instead, let me highlight three other claims. First, like others, I argue that Article 16 ought to be understood as a primary rule of international law in terms of the conceptual scheme the ILC laid down for itself. The key to understanding Article 16 is its generality as opposed to putative secondary nature. Second, I am not sure that the inclusion by the ILC of what is known as the double obligation requirement is defensible. The double obligation requirement – the demand that conduct of the principal state would be wrongful for the assisting state – may be insufficiently attentive to the interests of the international community in the integrity of treaty relations. And third, I argue that the exclusion of instigation from the ambit of complicity in the law of state responsibility is not supported by principle and, as a matter of positive law, may be incorrect.

State Complicity – Attribution, Participation, and Non-state Actors

Moving beyond inter-state complicity, the book then turns in Chapters 8 and 9 to consider state assistance to non-state actors. In some cases, particularly where the non-state actor is on the territory of the state, assistance of this kind may be swept up by wider due diligence obligations to prevent certain harms from occurring. But with respect to complicity specifically, there is a conceptual problem – without a principal wrong on the international plane committed by the non-state actor, there is no wrong for the putatively complicit state to be complicit in.

Chapter 8 discusses one way out of this problem – one that is evident in the decisions of certain human rights courts. The orthodox rules for the attribution of conduct to a state are marked by the search for a relationship of agency between the state and the non-state actor – either complete dependence or direction or control is required. In a series of cases, the Inter-American Court of Human Rights has lowered the standard for attribution to the state to encompass a complicit relationship between the state and the non-state actor. Likewise, the European Court of Human Rights, at least with respect to territorial cases, seems to have taken steps in a similar direction in El-Masri and Al-Nashiri. Although these approaches are somewhat understandable given the facts of the cases, in Chapter 8 I argue against such an attempt to address state participation of this kind by altering the general rules of attribution in international law.

In Chapter 9, I analyse the specific prohibition on state complicity in genocide, and, on the general level, propose what might be thought of as a non-state analogue to the rule in Article 16. This non-state analogue is, like the rule in Article 16, a general complicity rule. Working off the text of Article 16, I put forward a rule that reads:

A State which aids or assists a non-state actor in the commission of an internationally wrongful act by the latter is internationally responsible for doing so if:

(a) the State does so with knowledge of the circumstances of the internationally wrongful act; and

(b) the act would be internationally wrongful if committed by the State.

As the range of obligations binding non-state actors increases, so too does the potential to understand and prohibit states’ support for breaches thereof in terms of complicity. Given the different international legal nature of the principal actor, it is possible that the contours of the rule ought to differ from the rule in Article 16; the text above simply provides a starting point. But as to its bare existence, the essential logic of the rule in Article 16 justifies the recognition of its non-state analogue.


In conclusion, I will add two points. First, to treat individual and state complicity within the same framework is not to demand identical approaches. Nonetheless, such treatment does provide at least a starting point for comparative reflection on the structure and scope of the rules. Second, I am convinced by the significance for the international legal system of the relatively quick entrenchment of the general rule reflected in Article 16. The rule’s power lies, as Lowe put it, in its ‘bureaucratization of the monitoring of compliance with international law’ by states in their everyday relations.

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Sancho says

April 12, 2017

Thank you for your post. I had one question: is aiding and abetting synonymous with complicity in your view? There is some ambiguity on this issue in the context of genocide. Do you view them as the same thing or are they different? And if they are different, how are they different? Thanks!

Muhammad Ali Nasir says

April 12, 2017

A timely book. I hope it is read widely, which it deserves. First, I would like to know the extent to which complicity by omission requires that one intervene into a situation in order to end the occurrence or the possibility of that crime. Can one use then the idea of complicity in international criminal law terms to justify humanitarian interventions even when they are in violation of Article 2(4) of the UN Charter? Can one use the idea of complicity when a State A intervenes into a State B on B’s invitation to help it in a civil war, and when B (with the A’s support but not A’s consent) commits war crimes on its territory? This blog has an interesting discussion on the US airstrikes on the Assad regime’s airbase in Homs. Second, I would like to know the extent to which complicity is based on both the consequences and the intentions of actors. Suppose, states A, B, and C impose economic and diplomatic sanctions on a state D after destroying its core infrastructure because of which D faces a humanitarian catastrophe. To what extent D’s humanitarian situation involves the responsibility of A, B, and C (and involves complicity of E that only provided intelligence to A, B, and C so that they launch their airstrikes)? The humanitarian catastrophe in such a situation, it must be noted, is not a deliberate act but only emerges as a long-term consequence. What roles do motives and intentions play respectively in international criminal law in creating a distinction between collateral damage and war crimes? And, how does it engage the idea of complicity? Think of the sanctions against Iraq from 1990 to 2003. Think of Yemen at the moment. Third, I would like to know of the extent to which complicity as an idea in international criminal law varies, if at all, with the subject it is dealing with, i.e. the state and non-state actors, respectively. I believe that the open-endedness of motives leaves considerable scope for interpretation. What role, if any, do organizational capacity and political structures play? Or, is this irrelevant in international criminal law?

Federica Paddeu says

April 13, 2017

I don't think complicit means what you think it means ...

Humour aside, wonderful post - and book, which I have and have already read. Looking forward to the discussion!


Miles Jackson says

April 13, 2017

Hi Sancho,

Thank you. In my view, they are better understood as synonymous - I think the Semanza Trial Chamber [394] was correct when it held:

‘...there is no material distinction between complicity in Article 2(3)(e) of the Statute and the broad definition accorded to aiding and abetting in Article 6(1). The Chamber further notes that the mens rea requirement for complicity to commit genocide in Article 2(3)(e) mirrors that for aiding and abetting and the other forms of accomplice liability in Article 6(1).'

I discuss this at pages 93-97 of the book. Of course, other judgments, including the ICTY Appeals Chamber in Krstic, take the other view, though without clearly spelling out the difference. If there is difference, it will likely lie in a heightened mens rea for complicity in genocide under 2(3)(e) and 4(3)(e) of the Statutes.

More broadly, I think this problem flows only from the drafting peculiarities of the ICTR and ICTY Statutes and the attempt of the tribunals to make sense thereof. It does not arise under the Rome Statute or under customary international law.

Miles Jackson says

April 13, 2017

Hi Muhammad,

Thank you for your questions and comments. On the first question, in international criminal law the key to the omissions inquiry will be finding the existence of a duty on the individual and establishing that the failure to act had a substantial effect on the commission of the crime. In respect of the former, the possible sources of that duty are not altogether clear - I tried, in pages 103-107 of the book, to set out where such a duty to act may be grounded. In respect of the latter, the question is whether the omission had a substantial effect on the commission of the crime. In addition, what is required to fulfil the duty is limited by legal requirements.

This last point is relevant to the question about intervention - what either states or individuals are required to do is limited by other legal rules. In the Genocide Convention case, concerning the state obligation to prevent genocide, the ICJ held at [430]: 'The State’s capacity to influence must also be assessed by legal criteria, since it is clear that every State may only act within the limits permitted by international law; seen thus, a State’s capacity to influence may vary depending on its particular legal position vis-à-vis the situations and persons facing the danger, or the reality, of genocide.' In other words, it does not allow a violation of Article 2(4).

Regarding the hypothetical, there is certainly the possibility of responsibility for complicity if it is clear that State A is knowingly facilitating State B's war crimes.

On the second question, complicity ordinarily requires, in the first place, principal wrongdoing - we need to identify the principal wrong in which the putative accomplice is said to be complicit. The inquiry then turns more on the intentions of the accomplice at the time it rendered its assistance. As I note above, the fault element of accomplice liability is contested. However, if State A (or an individual) provided some assistance to another actor without any intention to facilitate wrongdoing or without knowledge that it was thereby facilitating that wrongdoing, the fact that the principal actor subsequently used the material to commit a wrong would not render the putative accomplice liable.

On the third question, there is scope for variation in the content of the complicity rules that bind states and individuals. In respect of the complicity obligations of states, either customary or conventional, there are difficult questions about how the elements of the complicity rule, particularly fault, play out. Pages 10 - 22, and particularly Page 17, of the Chatham House Report I mentioned above has a helpful discussion of that question. I hope this helps.


Federica - thank you. I should really amend the first sentence of the post!

Muhammad Ali Nasir says

April 14, 2017

Thank you, Miles.