[Editor’s Note: This article is part of a Just Security series, Prosecuting the Crime of Aggression Against Ukraine. All articles in the series can be found here.]

“The ultimate step in avoiding periodic wars, which are inevitable in a system of international lawlessness, is to make statesmen responsible to law. And let me make clear that while this is first applied against German aggressors, the law includes, and if it is to serve a useful purpose it must condemn, aggression by other nations, including those which sit here now in judgment.”

This is a quote from Robert Jackson’s opening speech of 21 November 1945 before the Nuremberg International Military Tribunal, a much celebrated and memorable speech delivered in the aftermath of the horrors of German wars of aggression. In view of Russia’s war of aggression against Ukraine, Jackson’s promise, made with direct reference to what was at the time – and following the coining of the term by Soviet Union law professor Aron Trainin – called “crimes against peace,” resonates louder than ever. It is certainly true that the prohibition of the use of force, by which the drafters of the UN Charter confirmed and developed the Briand-Kellogg Pact’s 1928 prohibition of war, had already before suffered from violations, including by States from the West. But taking together the clarity of the illegality, the intensity of the destructive violence and the overall goal to annex foreign territory, the seriousness of Russia’s violation of the prohibition of the use of force appears to be without precedent. It is therefore of central importance that international accountability efforts for Russia’s negation of this fundamental conduct rule of the international legal order include an international criminal justice response to the suspicion that “crimes against peace” have been and are being committed.

Precisely such a response, however, currently meets with an obstacle: There can be no doubt that President Putin and those, who together with him, allegedly are in a position effectively to exercise control over or to direct the Russian Federation’s political or military action, and planned, prepared, initiated or executed (and execute) this State’s war of aggression against Ukraine are under suspicion of having committed (and committing) the crime of aggression, as Nuremberg’s “crime against peace” is called today. Yet, by virtue of Article 15 bis (4) and (5) of the ICC Statute, the hands of Karim A. Khan, the Prosecutor of the International Criminal Court (ICC), are currently tied: In case of an act of aggression committed by a State, which, as the Russian Federation, has not acceded to the ICC Statute, the initiation of an investigation by the Prosecutor of the ICC depends on the UN Security Council referring the relevant situation to the Court pursuant to Article 15 ter in conjunction with Article 13 (b) of the ICC Statute. As long as President Putin will remain in office and hence in control of the exercise of Russia’s veto power in the UN Security Council, such a referral will not be forthcoming.

Things are different with respect to genocide, crimes against humanity and war crimes, as a result of Article 12 (2) and (3) of the ICC Statute. Here, the Prosecutor can exercise the Court’s jurisdiction also over nationals of a non-State Party if the relevant crimes were allegedly committed on the territory of a State Party or of a non-State Party that, as is the case with Ukraine, has accepted the Court’s exercise of jurisdiction. Prosecutor Khan is therefore currently left with no choice but to abstain from looking into the allegations that crimes of aggression have been committed. This means that he is compelled to conduct his investigations in a constricted fashion.

The crime of aggression’s special treatment in the situation of Ukraine reflects the frequently articulated sentiment of the distinct political sensitivity attached to this offense. In that connection, it constitutes a historical irony that France, Great Britain, and the United States, those three western powers who decisively contributed to the international criminalization of aggression, have grown skeptical concerning the international prosecution of this very crime. One reason for this reluctance likely is the awareness within the leadership of those states that some instances of their own use of force in the past fell within the grey area surrounding the prohibition of the use of force. This is one important reason why, at the 1998 Rome Conference on the establishment of the ICC, the crime of aggression came under the Court’s jurisdiction only at the very last moment and in the form of a mere placeholder, coupled with a mandate for further negotiations. Only at the first Review Conference on the ICC Statute, held in Kampala in the summer of 2010, those negotiations resulted in an agreement on the crime’s definition and, with one exception, on the conditions for the Court’s exercise of jurisdiction over the crime. It should take a couple of more years until, after a final round of difficult negotiations, the ICC’s Assembly of State Parties activated the Court’s jurisdiction over the crime of aggression as from 17 July 2018.

Although, taking existing customary international law into account, the elements of the crime were narrowly defined, excluding, most importantly, the existing grey area of the prohibition of the use of force, France and Great Britain did not show any breath of enthusiasm when they joined the consensus literally at the last moment. At least in part, this was likely due to the fact that those two States did not prevail with their demand, put forward together with the other three permanent members of the UN Security Council, to subject any proceedings before the ICC for the crime of aggression to an authorization by the Security Council and hence to the non-use of their veto powers. How to proceed in the absence of a green light by the Security Council, became the object of fierce negotiations. The majority of States Parties, among them most of the African and South American States, preferred the applicability of the same conditions for the Court’s exercise of jurisdiction as in the case of genocide, crimes against humanity and war crimes. This would have allowed the Prosecutor to initiate an investigation into an alleged crime of aggression in case of an alleged act of aggression against a State Party that had accepted the Kampala amendments. Also, a non-State Party having become the target of an act of aggression could have allowed the Court to exercise its jurisdiction over the crime of aggression through a declaration of acceptance of the ICC’s jurisdiction. But a group of predominantly western States, led by France and Great Britain, successfully insisted on a requirement of double consent to the Court’s exercise of jurisdiction in case of an alleged act of aggression of one State Party against another one. In order to avoid an asymmetrical treatment of State Parties, on the one hand, and non-State Parties, on the other hand, the Court’s power to exercise jurisdiction in case of alleged acts of aggression committed by non-State Parties was excluded altogether. It is this latter restriction of the Court’s scope of action, a restriction demanded not least by the United States, that presently benefits the Russian suspects in the Situation of Ukraine.

For a number of reasons, this situation is most unfortunate: In the Ukraine War, the initiation of the aggression constitutes the ‘original sin’ which opened the floodgate for thousands of atrocities that have given rise to allegations that war crimes may have been committed on a systematic scale as well as crimes against humanity and that, in certain cases, have even provoked a discussion about the commission of genocide. What is more, in many cases the crime of aggression is the only basis for attributing individual criminal responsibility for the targeting of Ukrainian soldiers and certain harms to Ukrainian civilians. Targeting Ukrainian combatants in the course of the hostilities does not amount to a war crime, a crime against humanity or genocide, and the same is true for causing incidental damage to Ukrainian civilians in the context of a military attack directed against a military object, unless the threshold of ius in bello disproportionality is passed. And then, there are Jackson’s words from Nuremberg: Russia’s war of aggression has subjected the prohibition of the use of force, a cornerstone of the UN Charter in the words of the International Court of Justice (ICJ), to a heightened risk of erosion. To avert such a risk constitutes a central purpose of the international criminalization of aggression.

In view of all that, there have lately been signs of an emerging change of mindset in international politics. Initially, the remaining weak spot in the international criminal justice architecture for the crime of aggression had not really become a matter of serious consideration. As if to avoid such consideration, the crime of aggression, despite the activation of the Court’s jurisdiction, was rather completely sidelined. In that vein, the European Union, in a number of official statements concerning the ICC even after 17 July 2018, simply avoided mentioning the crime of aggression, and the United States did not show any interest, either. As a result, the crime of aggression did not become an issue at the international stage even after Russia’s unlawful use of force against Ukraine in Crimea in spring 2014. Nothing changed in the course of the entire lead-up to the initiation of Russia’s war of aggression against Ukraine on 24 February 2022 and most governments did also not change direction even during several months to follow.

There is a wider background to this prevailing indifference: In the 1990s, when the idea of international justice experienced its revival, the crime of aggression had lost the sinister place at the apex of international criminality, which the Nuremberg Judgment had accorded to it by calling the waging of a war of aggression “the supreme international crime.” At the time, it had become widespread to consider the crime of aggression as conduct directed exclusively against foreign State sovereignty, and this international legal value had somewhat lost its appeal for quite a few observers at a moment in time where the protection of human rights had come into bloom in the international legal order. As a corollary, the struggle against impunity focused on “atrocity crimes” and, according to the predominant use of that term, only genocide, crimes against humanity and war crimes counted as such.

But soon after 24 February 2022, Ukraine’s legal diplomacy moved the crime of aggression into the center of the debate. More or less in parallel, interest in the crime of aggression has grown in international legal scholarship, too. In that context, more attention has also been given to the persuasive statement adopted by the UN Human Rights Committee in 2018 that State parties engaged in acts of aggression as defined in international law, resulting in deprivation of life, violate ipso facto the right to life under the Covenant for Political and Civil Rights.

Through the course of last year, governments eventually began recognizing that silence with respect to the crime of aggression is seriously problematic. On 2 March, the UN General Assembly adopted the historic resolution on “Aggression against Ukraine.” On 2 November, the UN General Assembly adopted, by consensus, a resolution in which the activation of the ICC’s jurisdiction over the crime of aggression is mentioned for the first time in a General Assembly resolution and in which the power of the Security Council to trigger proceedings before the ICC for all four crimes under the Court’s jurisdiction is noted. Thereafter, at last year’s Assembly of States Parties to the ICC Statute (ICC-ASP), Prosecutor Khan noted a renewed focus on the crime of aggression, and on 15 December 2022, the Council of the European Union directed its attention specifically to the Ukraine war and welcomed and encouraged further efforts to ensure accountability for the crime of aggression. The Council went on to stress that the prosecution of the crime of aggression is of concern to the international community as a whole.

The right conclusion to be drawn from this correct assessment would be to remedy the flaw at its roots and to improve the Statute of the ICC. For, this already existing, permanent international criminal court with a credible universal orientation constitutes the most appropriate institution for proceedings with respect to alleged crimes of aggression. In that vein, Prosecutor Khan, in his address to the last ICC-ASP, stated that “[w]hen we recognize that there is a gap in this architecture, in my view, we should try to address it through the Rome Statute.”

Three options for a reform are currently under consideration. Two of them consist of an amendment of the Kampala amendments: One could now take up the proposal, that had been supported by the majority of African and South American States, to align the conditions governing the Court’s exercise of jurisdiction over the crime of aggression with those applicable to the other three international crimes under the ICC’s jurisdiction. In their Buenos Aires Plan of Action of November last year, Parliamentarians for Global Action, have called upon governments to move in that direction and, already before, members of the Global Institute for the Prevention of Aggression, with Benjamin B. Ferencz as its President Emeritus, had made a similar appeal. A more modest alternative, also worthy of consideration, consists of allowing the Court to proceed with an investigation in case of an alleged act of aggression by a State Party not bound by the Kampala amendments or by a non-State Party against a State Party bound by the Kampala amendments or against a non-State Party that has accepted the Court’s jurisdiction if the UN General Assembly so recommends. The third option for reform consists of giving the General Assembly a more comprehensive role within the ICC system. Under this proposal, the Court would get the power to exercise universal jurisdiction not only in case of a referral of the relevant situation by the UN Security Council, but also if the UN General Assembly made such a referral in cases where the UN Security Council is prevented from taking action by a permanent member’s veto.

In all cases, it is legally conceivable to provide the revision of the ICC Statute with retroactive effect at least to 17 July 2018, the date of the activation of the Court’s jurisdiction over the crime of aggression. The amendment would only concern the conditions for the exercise of the ICC’s jurisdiction, while the crime of aggression as such formed part of customary international law already long before 2018. It is therefore not beyond imagination to improve the ICC Statute so as to overcome the legal obstacle that currently ties Prosecutor Khan’s hands with respect to the alleged crimes of aggression in the Situation of Ukraine. It is readily acknowledged that all the just-mentioned options for a reform of the ICC Statute involve complex legal issues, ranging from the powers of the UN General Assembly to the question of the entry into force of an amendment of a (Kampala) amendment. What is more, reform of the ICC Statute with a view to strengthening the jurisdictional regime governing the crime of aggression would require a number of States predominantly from the West to change their position taken thus far. Yet, the seriousness of the situation to which the Ukraine War has given rise warrants the effort of a demanding diplomatic initiative, and it should give every State sufficient reason to reconsider prior preferences.

The one important and complex political question that remains, however, is whether Russia’s war of aggression requires the decisive legal message implied in the initiation of criminal investigations to be sent out earlier than at that moment in time when a revision of the ICC Statute could realistically be put in place. This is where Ukraine’s demand, inspired by an early suggestion by Philippe Sands, for a Special Tribunal for the crime of aggression in the Situation of Ukraine, sets in. It is the idea to remedy the existing gap in the architecture of international criminal justice through the establishment of a transitional building block. The initiative to set up a Special Tribunal soon met with the approval of the European Parliament and the Parliamentary Assemblies of the Council of Europe, the OSCE and NATO. In the meantime, the debate has reached the inter-governmental level as well, especially, once Ursula von der Leyen, the President of the Commission of the European Union had embraced the initiative in principle in November last year. It cannot be doubted that a Special Tribunal falls behind the most stringent rule of law standards and that many national constitutions rule out the establishment of a tribunal ex post facto. Yet, in view of its far more decentralized structure, the situation has been and continues to be different at the international level and, accordingly, special tribunals have repeatedly played a significant role in the history of international criminal justice. Apart from the foundational role played by the International Military Tribunals of Nuremberg and Tokyo, it bears recalling that the Security Council based International Criminal Tribunals for the former Yugoslavia (ICTY) and Rwanda (ICTR) played a ground-breaking role when international criminal justice was reborn in the first half of the 1990s. One should also not forget the important contribution made by the Special Court for Sierra Leone early in the new millennium. While it is true that the establishment of the ICC implies the determination to move beyond the era of special international criminal tribunals, Russia’s war of aggression has laid bare that the jurisdictional regime for the crime of aggression under the ICC Statute remains insufficiently robust to render the call for a special tribunal superfluous. To the contrary, in this situation such a tribunal could, through the timely initiation of investigations, complement the ongoing work of the ICC in the common pursuit of the overarching goal to come up with a convincing response in terms of international criminal justice to the allegations that crimes under international law, including crimes of aggression have been and are being committed. A suitably worded agreement between the ICC and the special tribunal could ensure the adoption of a coordinated approach.

Over the past months, a number of models for the establishment of a special tribunal have been under consideration. On Monday of last week, Germany’s Foreign Minister Annalena Baerbock, in a speech delivered at the Hague Academy (German version; English version), expressed support for a hybrid tribunal, anchored in Ukrainian criminal law, but vested with an international component that could take different forms. A few days later, the United Kingdom went public with a statement pointing in the same direction. Yet, such an approach would have serious downsides: It would not address the crime of aggression as a crime under international law and hereby miss the point of why the prosecution of the crime of aggression is of concern to the international community as whole. Furthermore, as Minister Baerbock herself seems to recognize, it is likely that personal immunities under customary international law would shield President Putin in proceedings before such a tribunal. One should therefore look for a genuinely international solution, just as the European Parliament has now suggested in a Resolution, adopted by large majority last week.

This leads one to the clearly preferable model that envisages the conclusion of an international agreement between the UN and Ukraine, with the UN Secretary-General acting on behalf of the UN at the request of the UN General Assembly. This model is sketched out in clear terms in a non-paper whose current co-sponsors are Albania, Belgium, Estonia, Guatemala, Latvia, Liechtenstein, Lithuania, Luxembourg, Marshall Islands, North Macedonia, Poland and Ukraine. Admittedly, there is no international precedent neatly on point in all essential respects for such a course of action. The ICTY and ICTR were established by the UN Security Council; the international agreement between the UN and Sierra Leone pursuant to which the Special Court for Sierra Leone was set up, followed a recommendation to that effect by the UN Security Council (acting absent Chapter VII authorities); and the Extraordinary Chambers for Cambodia, while having been established pursuant to an international agreement between the UN and Cambodia, as recommended by the UN General Assembly, are incorporated in Cambodia’s judicial system in such a way that the character of these Chambers is not genuinely international. But the absence of a precedent which is directly on point in all essential respects does not make for a compelling argument against the model in question. To the contrary, this model rests on the solid legal assumption that the UN General Assembly would not hereby create jurisdiction over the crime of aggression, something that could be seen as a coercive measure and thus beyond the Assembly’s competences, in light of the ICJ’s advisory opinion in Certain Expenses. Instead, Ukraine as one of the territorial States of the crime and as the victim of Russia’s aggression, is vested with a jurisdiction title that it can entrust to an international tribunal for the purpose of adjudication. Beyond that, the crime of aggression, being anchored in customary international law, falls within an international criminal jurisdiction that is ultimately rooted in the international community as a whole. For those two reasons, the UN General Assembly would not vest the special tribunal with jurisdiction, it would only help activating the proper international exercise of an already existing jurisdiction. The General Assembly would, however, vest the special tribunal with a genuinely universal character. This would be relevant in one important legal respect: It would mean that the determination reached by the ICC Appeals Chamber in the case against al-Bashir that customary international law personal immunities enjoyed by acting heads of State, heads of government and foreign ministers are inapplicable before international criminal courts would apply also in the vertical relationship between relevant Russian suspects and the special tribunal. This would be much in the same way as the Appeals Chamber of the Special Court for Sierra Leone had found inapplicable Liberia’s customary right to personal immunity with respect to its then acting President Taylor. The endorsement by the UN General Assembly would also vest the special tribunal with precisely that degree of legitimacy that is highly desirable for the persuasiveness of the messages the tribunal’s work would be meant to send out. For, a positive vote by the General Assembly would constitute the most powerful confirmation possible that the investigation into allegations that crimes of aggression have been committed is indeed of concern to the international community as a whole.

Still, there is the valid and weighty critique of a selective activation of jurisdiction over the crime of aggression in the situation of Ukraine as long as other States, especially from the West, remain unprepared to treat the ICC’s jurisdiction over the crime of aggression with the same earnest as they do with the jurisdiction over genocide, crimes against humanity, and war crimes. The convincing response to this critique would be for State Parties to the ICC Statute to mobilize the necessary political will to remedy the existing statutory gap for the future through a revision of the Court’s founding treaty. Within such a two track approach, the special tribunal would be clearly marked as a transitional building block within the architecture of international criminal justice: Quite similar to the ICTY and ICTR, this special tribunal would not only adjudicate crimes under international law in the given situation, it would also help prepare the ground for moving international criminal justice forward – by paving the ground for the ICC to assume, in the future, its proper role in adjudicating, but preferably in preventing, the crime of aggression. In her speech of last Monday, Minister Baerbock has embraced such a two-track approach and she deserves much to be commended for her search of a principled course of action.

Whatever the political response to the question whether a timely message in terms of international criminal justice in the face of Russia’s ongoing war of aggression requires the establishment of a special tribunal, a diplomatic initiative in the spirit of Jackson’s Nuremberg promise to revise the ICC Statute is needed in any event. Or, in the words of Prosecutor Khan at the ICC-ASP of December last year, directed to the States Parties to the ICC Statute, it is imperative ”to explore how to strengthen this institution that you are collectively part of and that has been collectively built so that we can meet the needs of today, but also the requirements of tomorrow.”

IMAGE: Rescuers use special equipment in searching people trapped under the rubble of a high-rise residential building hit by a missile on January 15, 2023 in Dnipro, Ukraine. On January 14, Russia launched a new massive attack on Ukrainian cities. (Photo by Yurii Stefanyak/Global Images Ukraine via Getty Images)