While the outbreak of hostilities in Gaza has, to a large extent, pushed the ongoing conflict between Russia and Ukraine out of the headlines, it is imperative that the international community not lose sight of the importance of bringing Russia’s aggression to an end. As we have previously argued (see, for example, here and here), it is critical that those most responsible for Russia’s aggression are also held to account. This will require the establishment of a special tribunal given the comprehensive non-State Party carve out applicable in the case of State referrals and the fact that a United Nations Security Council referral will clearly not be forthcoming, meaning that the International Criminal Court (ICC) is unable to exercise jurisdiction over crimes of aggression committed in the context of the situation in Ukraine.
As we write, negotiations between Ukraine and its closest partners as to the shape of the proposed tribunal continue: in particular, while Ukraine has called for an international tribunal, to date, G7 States have only been willing to support an “internationalized,” or hybrid model. While the outcome of these negotiations remains uncertain, it is clearly agreed that, whatever the model, the tribunal’s jurisdiction would be limited to crimes of aggression committed on the territory of Ukraine.
These jurisdictional limitations have been deliberately designed to ensure that there would be no competition between the ICC and the proposed tribunal. Indeed, the ICC and the special tribunal should be seen as partners in the fight against impunity and the reinforcement of international law, and, as we have outlined in detail elsewhere, the two institutions can, and should, extend to each other the greatest possible cooperation.
Cooperation will clearly be required in the event the same person is indicted by both institutions. For example, Russian President Vladimir Putin is already subject to an ICC arrest warrant with respect to the war crimes of unlawful deportation and the unlawful transfer of parts of the population of an occupied territory outside that territory – and, for obvious reasons, he is a prime suspect in relation to the crime of aggression.
In this context, David Scheffer has suggested that “[t]he Rome Statute’s double jeopardy provision, Article 20(3) (‘Ne bis in idem’), presents a critical challenge.” Specifically, Scheffer argues that:
Article 20(3) may require the ICC to consider the STCoA’s initial prosecution of the crime of aggression against an individual in determining whether the same defendant can be charged by the ICC for conduct that overlaps both the crime of aggression and any other of the Rome Statute crimes: genocide, crimes against humanity, and war crimes.
For example, if a Russian general is tried before the STCoA for the crime of aggression because he plotted with other Kremlin leaders the military invasion of Ukraine in early 2022, but the same conduct approving the aggression plan also included, within that plan, strategizing the large-scale commission of war crimes by Russian forces inside Ukraine following the initial act of aggression, then Article 20(3) might be read by at least some ICC judges to prevent prosecution of the general for planning the commission of war crimes in Ukraine, whether or not he was convicted or acquitted before the STCoA on the charge of aggression.
We, however, are of the view that the principle of ne bis in idem embodied in Article 20 of the Rome Statute would in no circumstances bar the subsequent trial by the ICC of any person who has been finally tried for the crime of aggression by the special tribunal. And vice versa, the special tribunal would not be barred from trying for the crime of aggression any person who has already been finally tried by the ICC for genocide, crimes against humanity, or war crimes. Nor would such trials be prohibited by other ne bis in idem rules in international law. Four arguments, addressed in turn below, support this conclusion.
Article 20 of the Rome Statute Does Not Apply to Other International Criminal Courts
Ne bis in idem in Article 20(2) of the Rome Statute bars “another court” from trying a person for a crime within the ICC’s jurisdiction for which that person has already been convicted or acquitted by the ICC. Article 20(3) bars the ICC from trying a person for the same conduct that formed the basis for the person’s trial by “another court.” At first glance, the term “another court” in Article 20(2) and (3) is broad enough to encompass other international criminal courts. Indeed, some scholars adopt this reading and suggest that the ne bis in idem bar in Article 20(2) and (3) applies as between the ICC and other international criminal courts (e.g., Astrid Reisinger Coracini and Immi Tallgren in Triffterer’s Commentary to the Rome Statute, p 916). The context of the article, however, indicates that “another court” in Article 20 refers exclusively to the national criminal jurisdictions of States and does not apply to other international criminal courts.
To begin with, as a treaty, the Rome Statute is subject to the pacta tertiis rule, which stipulates that a treaty binds only parties and does not create obligations for a non-party State. The Rome Statute therefore can only bind States that are party to it and cannot impose obligations on a third party. Consequently, the bar on repeat trial in Article 20(2) can apply only to the criminal justice systems of State Parties to the Rome Statute. Article 20(2) does not create any obligation either for courts in non-party States or other international criminal courts to abstain from repeat trial for the same crime of a person who has already been tried by the ICC.
Conversely, the bar on repeat trial in Article 20(3) is directed at the ICC itself and applies once a person has been tried before “another court” for conduct constitutive of crimes falling within the ICC’s jurisdiction. As evident from the cross-reference in Article 17(1)(c), Article 20(3) forms part of the rules determining the admissibility of a case before the ICC. The admissibility rules enumerated in Article 17(1), in view of the reference to paragraph 10 of the Preamble and Article 1 of the Rome Statute in the chapeau to this provision, operate on the premise that the ICC is “complementary to national criminal jurisdictions” and that it is first and foremost for “the State which has jurisdiction” over a case to act. The admissibility rules in Article 17(1), including the one based on ne bis in idem, therefore apply to an ongoing or prior investigation or prosecution in a national criminal jurisdiction, either a State party or non-State party to the Rome Statute, with jurisdiction over relevant crimes. In contrast, a prior trial by another international criminal court does not trigger the application of ne bis in idem in Article 20(3).
Interpreting Article 20(3) of the Rome Statute as applying to prior proceedings before an international criminal court goes against the wording of the Rome Statute. It also suggests that international criminal courts are subject to the same rules as domestic courts, which is clearly not the case, precisely because the former are not part of a State’s legal system.
The ne bis in idem bar in Article 20(2) and (3) of the Rome Statute does, however, apply to the so-called “internationalized,” “hybrid,” or “mixed” criminal courts that are not independent international organizations with separate international legal personality, but which are formally anchored in a domestic judicial system of a State Party. Nevertheless, even if a hybrid model is employed, or if, contrary to the foregoing, the ICC’s judges take the view that, because of the broad reference to “another court,” Article 20 of the Rome Statute applies to another international criminal court, the ne bis in idem principle will not bar trial of the same person before both the ICC and the proposed special tribunal for the reasons that follow. (For a more detailed discussion of the term “another court,” see Gaiane Nuridzhanian, Ne Bis In Idem in Article 20(3) of the Rome Statute and Non-State Courts).
Not the Same Crime in Article 20(2)
As mentioned earlier, ne bis in idem in Article 20(2) bars another court from trying a person for a crime referred to in Article 5 of the Rome Statute (i.e., genocide, crimes against humanity, war crimes or the crime of aggression) if that same person has already been convicted or acquitted for that same crime by the ICC. The scope of ne bis in idem in Article 20(2) is limited to a prohibition on the subsequent trial for the “same crime”: it does not bar a subsequent trial for conduct characterized as a different crime. This reading of Article 20(2) clearly follows from its wording and is supported by the context of the provision. In particular, Article 20(2) uses the term “the same crime” in contrast to other ne bis in idem rules in the same article, namely Article 20(1) and (3) that bar a subsequent trial for the “same conduct.” This reading of Article 20(2) also follows from its interpretation in view of other relevant international law, and the provision’s drafting history (for details, see Nuridzhanian, The principle of ne bis in idem in international criminal law (Routledge 2024, forthcoming)).
As noted above, in relation to the situation in Ukraine, the ICC will not be able to try any person for the crime of aggression because of the non-State Party carve out, and the special tribunal’s subject matter jurisdiction would be limited to the crime of aggression. In other words, the crimes – understood here as culpable conduct and its legal characterization – tried before the proposed special tribunal and the ICC will not overlap. As Scheffer also acknowledges , the special tribunal would therefore not be barred by ne bis in idem in Article 20(2) from trying for the crime of aggression a person who has already been tried by the ICC for other crimes. In other words, Putin’s trial and conviction or acquittal by the ICC on the current charges of war crimes will not block his subsequent prosecution for the crime of aggression before the special tribunal. Nor would this assessment change in the event that Putin is charged with having committed other war crimes, or any crime against humanity or genocide.
What is more, Article 20(2) would not bar the special tribunal, or indeed any State Party to the Rome Statute, from trying a person for the same conduct that formed the basis for the person’s conviction or acquittal by the ICC, provided this conduct is legally characterized as a different crime.
Not the Same Conduct in Article 20(3)
As noted above, Article 20(3) provides that “[n]o person who has been tried by another court for conduct also proscribed under article 6, 7, 8, or 8bis shall be tried by the Court with respect to the same conduct” (emphasis added), unless the original proceedings were designed to shield a person from the ICC’s jurisdiction, or were otherwise not independent or impartial and were inconsistent with an intent to bring the person to justice. Clearly, what is of relevance here are the acts or omissions of the person being tried, not the legal characterization of that conduct as a particular crime.
It is now well established in case law that a specific act or omission of a defendant (for example, the deliberate killing of civilians) may be characterized as the war crime of wilful killing (assuming the conduct took place in the context of an international armed conflict and provided those killed were protected by the Geneva Conventions), as well as genocide (so long as the perpetrator had the requisite special intent) and the crime against humanity of murder (so long as the killing was committed as part of a widespread or systematic attack directed against any civilian population with knowledge of the attack). Similar Venn diagrams could be drawn in relation to a range of other conduct criminalized under Articles 6, 7, and 8 of the Rome Statute.
As noted above, Scheffer suggests that plotting the military invasion of Ukraine and strategizing in the same meeting in relation to the large-scale commission of war crimes would amount to the “same conduct,” which he implies could give rise to individual criminal responsibility for both the crime of aggression and one or more (unspecified) war crimes, thereby potentially engaging Article 20(3) (while acknowledging that if the intent to commit war crimes arose weeks or months later, independent of the plan to invade Ukraine, Article 20(3) “should be no impediment”).
Scheffer’s example, however, involves a simple coincidence of time and place in the occurrence of two separate acts. The defining feature of the crime of aggression is the State act element of the crime (a violation of the prohibition of the use of force that amounts to a manifest violation of the U.N. Charter). This constitutes the point of reference for the definition of what makes a person individually criminally responsible for the crime of aggression. That is, a person must have planned (or prepared, initiated, or executed) the State act of aggression. Engaging in the planning of other crimes, even if undertaken at the same time and in the same place, is factually distinct conduct. A discussion about instructions to be given to armed forces about their rules of engagement, or the fact that troops will not be prosecuted for violations of international humanitarian law, or about the strategic or operational benefits of the large-scale commission of war crimes (for example, that it might weaken the victim population’s morale and ability to resist and cause a victim State to surrender) is simply not the same conduct as planning a State act of aggression.
Planning instead requires participation in meetings during which plans for a prohibited use of force are formulated. A causal nexus between the planning and the relevant State act of aggression is likely also to be required – it is expected that, consistent with the approach of the International Military Tribunal, the ICC will require planning acts to amount to a substantial step towards the carrying out of the crime of aggression in order to attract individual criminal responsibility (see, Carrie McDougall, The Crime of Aggression under the Rome Statute of the International Criminal Court).
Considered from another angle, unlike the definition of other Rome Statute crimes, the collective act (the State act element of the crime of aggression) is not broken down into underlying individual conduct (such as killing, rape, or torture) – which is where the overlap in conduct arises in relation to other Rome Statute crimes. Indeed, it is important to recall in this context that the contextual elements of other Rome Statute crimes do not require proof that a person was engaged in the planning of the commission of mass crimes. For example, the Rome Statute definition of crimes against humanity requires that an underlying act be “committed as part of a widespread or systematic attack directed against any civilian population, with knowledge of the attack.” There is no requirement that the perpetrator was him or herself responsible for the widespread or systematic attack. Technically, a single murder can be a punishable wrong so long as all applicable elements are satisfied. Similarly, while the Elements of genocide controversially require that “the conduct took place in the context of a manifest pattern of similar conduct directed against that group or was conduct that could itself effect such destruction,” there is no requirement per se that an individual was themselves responsible for such a manifest pattern of conduct.
The situation in relation to war crimes is even more stark given that Article 8(1) provides that “the Court shall have jurisdiction in respect of war crimes in particular when committed as part of a plan or policy or as part of a large-scale commission of such crimes.” In other words – this is clearly a (potentially dispensable) jurisdictional limitation – not a requirement that must be established to prove individual guilt. In practice, the ICC Office of the Prosecutor has focused its attention on individuals who have orchestrated the commission of mass crimes because their culpability is considered to be greater. This is, however, a policy issue, relating to the selection of defendants. That an individual defendant orchestrated the commission of a range of crimes will also be relevant to the theory of individual criminal responsibility that is applicable (such as indirect co-perpetration) – but again, this is an issue that is conceptually distinct from the question of whether the “same conduct” gave rise to one or more Rome Statute crimes.
Policy reasons further suggest that it would be inappropriate to artificially characterize the planning of a State act of aggression and the planning of the mass commission of war crimes (or any other Rome Statute crimes) as “the same conduct.” The crime of aggression is an all-encompassing wrong that opens the door to the commission of other Rome Statute crimes. Aggression attracts criminal sanction because of the harm it causes to international peace, State sovereignty, and the safety and security of a State’s population. A prosecution for crimes other than aggression could simply not capture the totality of the wrong reflected in the crime, which in this context militates against an overly broad interpretation of the reference to the “same conduct” in Article 20(3).
For these reasons, no prosecution before the ICC for war crimes, crimes against humanity, or genocide would include “the same conduct” as would form the basis for any prosecution of a crime of aggression, whether that be before an international or hybrid special tribunal.
Other Relevant International Law Rules
In international law, the principle that no person shall be tried twice in the same matter is embodied in intra-jurisdictional and inter-jurisdictional ne bis in idem rules.
The intra-jurisdictional ne bis in idem rule applies within one and the same domestic or international criminal jurisdiction. Article 20(1) of the Rome Statute is an example of an intra-jurisdictional ne bis in idem rule. The provision prohibits the ICC from repeatedly trying the person for the same culpable conduct for which the person has already been convicted or acquitted by the ICC. In international human rights law, at least as reflected in the International Covenant on Civil and Political Rights (ICCPR) (Article 14(7)) and the European Convention on Human rights (ECHR) (Article 4 of Protocol 7), the bar on repeat trial for the same offence is also limited to the exercise of jurisdiction by one and the same State. The text of these provisions clearly indicates that ne bis in idem rules in the ICCPR and the ECHR oblige the one and the same State not to try the same person for the same crime twice, but impose no such restrictions on repeat trial of the same person for the same conduct in two or more different States. By persuasive analogy, ne bis in idem in international human rights law bars one and the same international criminal court from trying the same person twice for the same matter. However, ne bis in idem in international human rights law does not have an inter-jurisdictional reach and does not therefore apply as between two international criminal courts such as the ICC and the proposed special tribunal.
In contrast to intra-jurisdictional rules, the inter-jurisdictional ne bis in idem applies between different criminal jurisdictions, be it domestic or international. The inter-jurisdictional ne bis in idem prohibition exists primarily as a treaty-based rule. Article 20(2) and (3) of the Rome Statute discussed earlier is an example of ne bis in idem applicable between an international criminal court, on the one hand, and a domestic criminal jurisdiction, on the other. But no customary international law ne bis in idem rule applicable between different criminal jurisdictions – and that would apply as between the special tribunal and the ICC – has emerged to date. Customary international law therefore does not impose any bar on subsequent trial by the special tribunal of persons that have already been tried by the ICC, or vice versa.
As demonstrated by the foregoing, the better interpretation of Article 20 of the Rome Statute is that the ne bis in idem principle would not be an impediment to the trial of the same person before both the ICC and the proposed special tribunal for crimes of aggression committed on the territory of Ukraine. A person could lawfully be prosecuted by the proposed special tribunal for one or more crimes of aggression committed on the territory of Ukraine, and they could also be prosecuted by the ICC for war crimes, crimes against humanity and/or genocide.
Indeed, in the case of a leading suspect such as Putin, a compelling case can be made that he should be held to account for the crime of aggression before an ad hoc tribunal, in addition to his prosecution for the war crimes with which he has already been charged, and any additional charges that might be unveiled by the ICC in coming months. A prosecution for the crime of aggression would capture the totality of the wrong committed. It would also take into account the fact that the victims of Russia’s aggression are not limited to civilians but include Ukrainian combatants, as well as members of the Russian forces who have at least in some cases been induced to fight a war on false premises or indeed are fighting under duress. Indeed, it is arguable that the indirect victims of Russia’s aggression extend to all those who have been affected by the food and energy crises caused by the conflict, as well as those States whose national interests have been threatened by the unprecedented attack on the international order. Justice can only be delivered to this full range of victims through a crime of aggression prosecution.
While we do not believe that ne bis in idem is a bar to the prosecution of anyone in relation to the situation in Ukraine before the ICC and the proposed special tribunal, this is not to say that the principle is irrelevant. The prohibition on repeat trials for the same conduct is a general principle of law and a fundamental human rights guarantee. In view of this, and in light of the number of domestic investigations into crimes of aggression committed against Ukraine that have been opened, the statute of the special tribunal should include clear rules limiting the possibility of future trial by the tribunal of any person who has been tried for the same crime in other domestic or international courts, provided such trials were genuine and were not intended to shield the person from criminal responsibility for the crime of aggression.
For an in-depth examination of Article 20 Rome Statute, see Gaiane Nuridzhanian, The principle of ne bis in idem in international criminal law (Routledge 2024)
For more detail on the proposed special tribunal, see Carrie McDougall, ‘The Imperative of Prosecuting Crimes of Aggression Committed Against Ukraine’ (2023) 28:2 Journal of Conflict and Security Law, 203-230, https://doi.org/10.1093/jicj/mqad035; ‘Why Ukraine Needs and International – Not Internationalised – Tribunal to Prosecute the Crimes of Aggression Committed Against It’ (2023) Polish Review of International and European Law (forthcoming).