The Special Tribunal for the Crime of Aggression Against Ukraine in the European Legal Space

Table of Contents: 1. Introduction. – 2. The timeline of the creation of the Special Tribunal. – 2.1. On the desirability of the Tribunal. – 2.2. Mobilising international support (2014–2023). – 2.3. Towards formalization: the Council of Europe Framework (2023–2025). – 3. Key features of the Special Tribunal. – 3.1. Jurisdiction: a narrow and focused mandate. – 3.2. Immunities: a pragmatic compromise heeding to state sovereignty. – 3.3. Due process: consistency with the right of defence. – 4. The tribunal of European law: selected issues. – 4.1. The Council of Europe and European Law. – 4.2. A tension with the autonomy of EU Law?. – 4.3. Relationship with the ICC and the development of international law. – 5. Conclusion.

Abstract: The Special Tribunal for the Crime of Aggression against Ukraine, set up in 2025 by agreement between the Council of Europe and Ukraine, is an ad hoc criminal court tasked with investigating and prosecuting the crime of aggression against Ukraine. The purpose of the article is to introduce scholars of EU law to the main debates that took or take place, among international lawyers, about the Tribunal, and to reflect on the interplay between the Tribunal and European law. The article first discusses the process and circumstances of its creation, highlighting the role of the European Union. Then it discusses salient features of the Tribunal: issues of jurisdiction, immunities, and fair trial, showing the structural compromises that they embody. The analysis further situates these features within the broader European legal space, zooming on the Tribunal’s necessary alignment with European Convention on Human Rights standards, a potential (although unlikely) conflict with the autonomy of EU law, and the possible consequences for EU Member States’ cooperation obligations. By foregrounding these issues, the article contributes to current debates on the EU’s role in international criminal justice and the constitutional limits of its external action.

Keywords: Special Tribunal for the Crime of Aggression Against Ukraine – international criminal law – European Union law – European Convention on Human Rights – immunities – trial in absentia.

1.   Introduction

The Special Tribunal for the Crime of Aggression against Ukraine is an ad hoc criminal court established in June 2025 by a historic agreement between the Council of Europe and Ukraine.[1] Its task is to investigate and prosecute people who bear the ‘greatest responsibility’ for planning, preparing, initiating, or executing the act of aggression against Ukraine.[2] The Tribunal is empowered to conduct investigations, issue indictments and arrest warrants, conduct trials (including, as it is likely to happen in most cases, in the absence of the accused), and deliver judgments.[3] Its jurisdiction is specifically tailored to address the ‘aggression gap’ in international criminal law, as the International Criminal Court (ICC) is prevented by its own jurisdictional rules from prosecuting this specific crime in the context of Ukraine,[4] and amending the ICC statute is politically infeasible, at least within a time-frame that would enable meaningful accountability to be established in this context.[5] The Tribunal shall apply in the first place its Statute and rules of evidence to be adopted by the judges; in the second place, relevant international law; and, failing that, provisions of substantive Ukrainian criminal law relating to the crime of aggression.[6]

The establishment of the tribunal was premised on the belief that Russia’s full-scale invasion on 24 February 2022 constituted a violation of the United Nations Charter[7] that must be punished.[8] The European Union’s involvement was substantial: the European Commission and the European External Action Service (EEAS) played notable roles in drafting the foundational legal instruments, including the Agreement on the Establishment of the Special Tribunal and its Statute.[9]

Even though the EU is not a party to the agreement, an analysis from the perspective of the Tribunal’s implications for the EU and European legal order – which is this article’s distinctive contribution – is warranted for two reasons: first, the Council of Europe and the EU have significantly overlapping membership, some common aims, and their legal orders are deeply intertwined; second, the EU’s deep institutional investment in the Tribunal’s creation marks a defining moment in its evolution as a global legal actor, yet it simultaneously gives rise to constitutional questions. While much has been written on the general feasibility and legitimacy of such a tribunal,[10] the purpose of the article is to introduce scholars of EU law to the main debates that took or take place, among international lawyers, about the Tribunal, and to reflect on the interplay between the Tribunal and European law. 

To this aim, the second Section traces the timeline of the Tribunal’s establishment, paying particular attention to the role of the EU. The third Section reviews the principal arguments surrounding the Tribunal’s formation. It shows that the final form of the Tribunal owes to a proposal by the EEAS. The fourth Section outlines debates surrounding some of the Tribunal’s key features. Finally, the fourth Section examines the interplay between the Tribunal and key areas of EU law: first, in light of the interplay between the Council of Europe and EU law, including the latter’s perspective accession to the former; second, the Tribunal’s implications for the autonomy of EU law; third, its significance for the EU’s efforts in international criminal justice. It then draws to a conclusion.

2.   The timeline of the creation of the Special Tribunal

2.1.  On the desirability of the Tribunal

The debate may be summed as follows: on the one hand, there exists the teleological imperative to vindicate the prohibition of aggression and to ensure individual criminal accountability for its manifest breach. As the debate in the European Parliament shows, beyond the legal and moral dimensions, the Tribunal is also (meant to be) seen as a powerful political tool to signal a united and unwavering resolve to uphold the principles of international law and to counter any attempts at ‘business as usual’ with the aggressor State, thereby reinforcing the international legal order and deterring future acts of aggression.[11] On the other hand, counterarguments invoke the perennial spectre of selectivity and double standards in international justice:[12] for example, why no comparable effort was made to prosecute the leaders responsible for the 2003 invasion of Iraq?[13] Another problem is that, for the Tribunal to be seen as legitimate, some argued it would require broad international support, ideally through a UN General Assembly resolution backed by a significant majority of States from all regions: without this global buy-in, the Tribunal risks being perceived as a regional or bloc-based court, lacking the universal standing necessary to speak for the international community as a whole. Finally, there are concerns that creating a new ad hoc body could lead to the fragmentation of international criminal law, diverting resources and political capital away from the permanent system of the ICC.[14] For the EU, as a staunch supporter of the ICC, this required a delicate balancing act. As this article intends to show, the final design of the Special Tribunal as a narrowly focused court, working in synergy with the ICC, reflects a deliberate effort to address these concerns.

2.2   Mobilising international support (2014–2023)

The Special Tribunal is the culmination of years of negotiation to address an accountability gap in international criminal law.[15] The Russian full-scale invasion in February 2022 was immediately condemned by the European Council as an ‘aggression’,[16] and the international rhetoric against Russia was much stronger than it had been in 2014.[17] While the ICC Prosecutor quickly opened an investigation into war crimes, crimes against humanity, and genocide, there is a critical jurisdictional lacuna: in this context, the ICC lacked authority to prosecute individuals for the crime of aggression due to the specific limitations in the Rome Statute.[18]

Initially, a clear commitment to holding perpetrators accountable was demonstrated by the swift creation and expansion of the Joint Investigation Team,[19] an evidence-gathering coalition, initiated by Ukraine, Lithuania and Poland, promptly joined by four other nations (Estonia, Latvia, Slovakia and Romania) and strengthened by the involvement of the ICC, Europol, and a cooperation agreement with the United States. Domestically, the Office of the Prosecutor General (OPG) of Ukraine started to document war crimes allegedly committed by the Russian army in Ukraine.[20] The EU, in coordination with the UK and US, established an Atrocity Crimes Advisory Group, to support the Ukrainian OPG. The Ukraine accountability conference in The Hague (July 2022) was another important stepping stone: Members of the Council of Europe agreed on matters relating to evidence collection and support to ongoing investigation, and committed to establish a dialogue group on accountability for Ukraine.[21]

The idea of a special tribunal gained public traction already in March 2022, led by Ukrainian officials,[22] as well as politicians and international lawyers.[23] The Parliamentary Assembly of the Council of Europe (PACE) became the first international body formally to call for such a tribunal in April 2022.[24] Throughout 2022, Ukraine, with steadfast support from Baltic and other Eastern European States, spearheaded a diplomatic campaign to build international backing.[25]

Within the EU, a consensus was not immediate. There was ambiguity on the desirability and the form of the Tribunal. In May 2022, the European Parliament issued a Resolution calling for the establishment of the Tribunal,[26] but key Member States like France and Germany initially expressed reservations, reflecting a wider caution among G7 States about the precedent that a fully international (as opposed to hybrid) tribunal might set.[27] There was, in sum, a tension between the principled demand for justice from Eastern Member States and the more pragmatic, precedent-wary stance of others. This entailed disagreement on the nature of the tribunal: while Ukraine and many States (including Belgium and Luxembourg) advocated for a fully international tribunal created via a multilateral treaty and endorsed by the UN General Assembly to ensure its legitimacy and ability to overcome immunities, a counter-proposal emerged, reportedly from the G7, for a ‘hybrid’ or ‘internationalised’ court rooted in Ukraine’s domestic legal system.[28] This latter model was heavily criticised for being unable legally to override head-of-State immunity, a fatal flaw for a tribunal whose primary targets are the highest-ranking leaders.[29] The European Commission long hesitated between an ad hoc international tribunal and the specialised ‘hybrid’ court, offering support for either option.[30] Recognizing the futility of pursuing a UN Security Council-mandated tribunal, which Russia would veto, supporters opted for a more pragmatic route.[31] In September 2022, the Council of Europe ‘noted with interest’ the Ukrainian proposal for the establishment of a Tribunal.[32]

2.3   Towards Formalization: The Council of Europe Framework (2023–2025)

The choice was made to pursue the tribunal within the Council of Europe (not UN) framework, as the Council had already expelled Russia and was seen as a venue with both legitimacy and flexibility. The European Parliament also added its voice, passing a resolution that endorsed the Tribunal.[33] Since January 2023, an informal coalition of State representatives (the ‘Core Group’), met to negotiate on the founding instruments of the Tribunal. A significant step, driven by the European Commission, was the establishment of the International Centre for the Prosecution of the Crime of Aggression against Ukraine (ICPA) at Eurojust in July 2023, which provided an EU-supported forum for preparatory work and evidence collection.[34] Within the Core Group, an impasse was reached due to legal challenges to the international model (within UN framework) and the purely hybrid model (which the Ukrainian Constitution does not allow)[35]. The EEAS proposed a further alternative, which is in essence the final form of the Tribunal, namely that: ‘the Tribunal should be set up by a multilateral agreement between the Core Group-participating states and receive international legal personality. At the same time, the Tribunal’s independent prosecutor should only investigate cases if the Prosecutor-General of Ukraine transfers relevant Ukrainian criminal proceedings to the Tribunal’.[36]

The technical work of the Core Group culminated, after fourteen meetings, in the Lviv Statement of 9 May 2025, which formally marked the conclusion of the drafting phase for the Tribunal’s legal instruments. This statement explicitly acknowledged the significant contribution of the European Commission and the European External Action Service in drafting the Tribunal’s Statute and founding Agreement, which highlights the EU’s deep institutional investment in the project. The final, decisive step occurred on 25 June 2025, when the Council of Europe and Ukraine signed the Agreement establishing the Special Tribunal, which simultaneously entailed the adoption of its Statute. 

Ultimately, the Tribunal has an element of hybridity:[37] it has international judges,[38] tasked with applying first and foremost international law and to ensure compliance with international law,[39] but it is based on Ukrainian territorial jurisdiction, investigation starts only with a request of the Ukrainian Prosecutor General,[40] and it might apply substantive provisions of Ukrainian national law. 

3.   Key features of the Special Tribunal

The Statute of the Special Tribunal establishes an institution whose core features (jurisdiction, approach to immunities, and due process guarantees)[41] reflect the attempt to create an effective and legitimate court in the circumstances – and facing the objections – briefly recalled in the previous Section. 

3.1.  Jurisdiction: a narrow and focused mandate

The Tribunal’s jurisdiction is intentionally narrow, a direct response to the specific ‘aggression gap’ it was created to fill. Its subject-matter jurisdiction is limited to the ‘crime of aggression against Ukraine’.[42] The definition of this crime in Article 2(1) of the Statute is identical to that of Article 8 bis (1) of the Rome Statute, namely ‘the planning, preparation, initiation or execution, by a person in a position effectively to exercise control over or to direct the political or military action of a State, of an act of aggression which, by its character, gravity and scale, constitutes a manifest violation of the Charter of the United Nations’. 

This avoids creating a new definition of the crime. There is nonetheless an element of novelty.[43] The Statute does not specify a list of acts counting as aggression (Article 8 bis (2) Rome Statute), but merely that the Special Tribunal ‘shall take into account United Nations General Assembly Resolution 3314 (XXIX) of 14 December 1974 and all relevant United Nations General Assembly resolutions with respect to Ukraine, including those recited in the preamble of the Agreement between the Council of Europe and Ukraine on the Establishment of the Special Tribunal for the Crime of Aggression against Ukraine’. 

It is possible that the Special Tribunal and the ICC will develop two strands of case law on what constitutes ‘aggression’ that runs on parallel, or anyway divergent, paths: the decision of one court is not binding on the other, and Article 5 Statute contains a non-affectation clause for ‘existing or developing rules of international law’. 

Its jurisdiction ratione loci is also limited (for the ‘crime of aggression against Ukraine’), and ‘based on the territorial jurisdiction of Ukraine’ (Article 1 Statute). Ratione temporis, there is, however, no limit. Any aggression against Ukraine, past or future, is within the jurisdiction of the Tribunal. This presumably includes facts that took place in 2014 as well as 2022.[44]

This specialised jurisdiction is a direct answer to the critique that the Tribunal might needlessly duplicate the work of the ICC: it will not. By focusing only on what the ICC cannot (for the foreseeable future) prosecute, the Special Tribunal is designed to be complementary, not competitive. It does not encroach on the ICC’s ongoing investigations into war crimes, crimes against humanity, or genocide. 

Its personal jurisdiction is also restricted to the prosecution of ‘persons who bear the greatest responsibility’ for the crime (Article 1 Statute). This formulation, not uncommon in international criminal law,[45] is a legal standard of considerable ambiguity, the precise contours of which must be delineated by the Tribunal’s own jurisprudence (and perhaps the practice of the Ukrainian Prosecutor General). This task is likely to result in the Tribunal confronting a series of fundamental legal questions of the kind that other international courts have. First, an interpretative question arises as to the very meaning of ‘greatest responsibility’. Does this standard refer exclusively to the formal apex of the State’s political and military hierarchy, or does it admit of a more functional interpretation, potentially encompassing individuals outside the formal chain of command whose influence was nonetheless decisive in the planning, preparation, initiation, or execution of the act of aggression? The ICC’s case law allows either interpretation.[46] The Rome statute requires that a crime be of sufficient gravity as a condition for admissibility (Article 17(1)(d) Rome Statute).[47] As part of the review of that condition of gravity, in the Kenya situation (the Prosecutor’s first proprio motu investigation) the Trial Chambers have held that the Prosecutor must carry out ‘a generic examination of […] whether such groups of persons that are likely to form the object of the investigation capture those who may bear the greatest responsibility for the alleged crimes committed’.[48]These people included those selected by the Prosecutor by reference to their roles in ‘inciting, planning, financing, colluding with criminal gangs, and otherwise contributing to the organization of the violence’ (which suggests a formal criterion).[49] Later, in the Mavi Marmara context, the pre-trial Chamber followed a different approach: the determination of who bears the greatest responsibility does not depend on a person’s rank or seniority, but rather on their actual role in the commission of the crimes.[50]

Second, an evidentiary question follows: what specific threshold must the Tribunal’s Prosecutor cross to establish not only that an individual was ‘in a position effectively to exercise control’ but that their responsibility was of the ‘greatest’ degree? This will require the Chambers to develop a coherent and principled typology of culpability, distinguishing the architects of the crime from its mere instruments, a distinction that is not self-evident. 

3.2. Immunities: a pragmatic compromise heeding to state sovereignty

Article 23(4) of the Statute explicitly States that functional immunity shall not apply before the Special Tribunal. This is a crucial provision, reflecting the growing international norm that immunity for official acts does not extend to crimes under international law. It is also logical, because preventing the Tribunal from prosecuting those who ordered the aggression (in the highest echelons of the chain of command), would run counter to the very purpose of establishing the Tribunal. 

However, the Statute takes a more cautious approach to personal immunity. Article 23(5) effectively recognises the personal immunity of serving heads of State, heads of government, and ministers of foreign affairs (the ‘troika’). It stipulates that an indictment against such individuals cannot be confirmed by a judge while they remain in office, unless their immunity is waived. This provision prevents the issuance of arrest warrants and the commencement of trials against these sitting officials, but not their indictment.[51]

This was a key point of contention. On the one hand, in fact, one could take a view that, under customary international law, there are no exceptions to functional immunity.[52] On the other hand, that view stands in stark contrast to the position authoritatively articulated by the International Criminal Court in its seminal Al-Bashir judgment, where the Appeal Chambers concluded that customary international law recognises no such immunity for a head of State before an international court.[53] While it means that the highest-ranking leaders cannot be prosecuted while in power, the Statute ensures that the Tribunal can proceed against them once they leave office (or if their immunity is waived), as their functional immunity for the acts committed will not apply.[54] It also means they can be indicted – but that their indictment cannot be confirmed. 

3.3.  Due process: consistency with the right of defence

The Statute contains extensive due process guarantees to ensure that its proceedings are fair and consistent with international human rights standards, in particular the right of defence. These include the presumption of innocence, the right to legal assistance, and the right to examine witnesses (Articles 18, 19 and 20 of the Statute). Three features are particularly salient, as noted also by Nuridzhanian.

First, Article 28 allows for trials in absentia, but only under strict conditions. Such a trial can only proceed if the accused has unequivocally waived their right to be present or if all reasonable steps have been taken to inform them of the charges and secure their appearance. Crucially, any person convicted in absentia has the absolute right to a full retrial in their presence should they later come into the Tribunal’s custody (Article 28(3) of the Statute). This provision is ‘existential’. It preserves a raison d’être for the Tribunal. How likely it is that Russia surrenders the accused to the Tribunal? Absence of the accused will not prevent the Tribunal from going ahead with the trial. Likely, most if not all trials will be in absentia.

Ukraine has been convicting individuals in absentia during the war under national law,[55] but the legality of this practice under international law is by no means uncontested.[56] On the one hand, Article 14(3)(d) International Covenant on Civil and Political Rights, to which Ukraine is a party, guarantees the defendant a right ‘to be tried in his presence and to defend himself in person or through legal assistance of his own choosing’, and the Rome Statute prohibits trials in absentia, in its Article 63. On the other hand, the Council of Europe’s position has been, throughout the negotiations for the Special Tribunal, that trials in absentia should be allowed in the interests of justice. Article 6 European Convention on Human Rights[57] (of which Ukraine is a party) does not contain an absolute right for the accused to a trial in presentia,[58] and the case law of the European Court for Human Rights is that such trials are possible but a retrial must be guaranteed in case of doubts over the defendant’s knowledge of the proceedings or of the verdict.[59]

In the present author’s opinion, the opportunity to conduct trials in absentia is a regression from the standards of international criminal justice,[60] but it is necessary if the Special Tribunal is to carry out trials. This regression is mitigated by the right to request the reopening of proceedings if they had not previously waived their right to appear or accepted the initial judgment – but it may still have a negative impact upon the Tribunal’s credibility. This latter point is more of a question about the political wisdom of trials in absentia than about their legality.

Second, the principle of ne bis in idem in Article 17 is designed to prevent double jeopardy and manage the Tribunal’s relationship with other courts. It bars the Tribunal from trying a person for the same conduct for which they have already been tried by a national court, unless those proceedings were a sham designed to shield the person from justice, or when they were otherwise not conducted impartially. Presumably, this will be for the Tribunal itself to establish on a case by case basis. Under the Statute, this objection would be raised as a preliminary motion challenging the Tribunal’s jurisdiction. The accused is entitled to ‘raise defences’,[61] which must include the right to invoke the ne bis in idem protection of Article 17, before the Trial Chamber. The Trial Chamber’s ruling on such a jurisdictional challenge can then be appealed by either the person indicted or the Prosecutor. This procedural framework is comparable to that of the ICC, where challenges to the admissibility of a case, including on ne bis in idemgrounds (under Article 20 of the Rome Statute), are typically brought as preliminary motions. The jurisprudence of the ICC may offer limited guidance, because although it delineates a sharply defined perimeter for the application of the ne bis in idem principle, the Rome Statute does not contain provisions on sham proceedings.[62] Central to the ICC case law is that the principle’s protection, enshrined in Article 20 of the Rome Statute, is triggered only where there has been a trial ending in a judgment on guilt or innocence, and procedural terminations or dismissals without such a merits judgment do not suffice.[63] The Special Tribunal could apply the in concreto test, that is, focusing on the ‘same conduct’, rather than the focusing, in abstracto, on the formal legal characterization of an offense – this is a choice that aligns it with the Rome Statute and distinguishes it from the older ad hoc tribunals. In evaluating prior national proceedings, however, the Tribunal’s case law will necessarily have to develop standards for its ‘sham trial’ exceptions, providing substantive meaning to the concepts of proceedings intended to ‘shield’ a person or those not conducted impartially. In establishing the standards for these ‘sham trial’ exceptions, the Tribunal might conduct a teleological inquiry into the prosecutor’s intent. The criterion for impartiality and due process, in turn, would be benchmarked against the norms recognised by international law,[64] requiring the identification of fundamental defects that vitiated the integrity of the proceedings and demonstrated an objective failure to adhere to the essential tenets of a fair trial.[65] Finally, it is also worth noting that Article 17(4) Statute explicitly forbids a subsequent trial by a national court of Ukraine for the same conduct. 

A third noteworthy feature is the role of the Prosecutor General of Ukraine, who plays a gatekeeping, national‑coordinating role vis‑à‑vis the Special Tribunal’s Prosecutor. Article 23(1) of the Statute provides that ‘the Prosecutor General of Ukraine refers to the Prosecutor of the Special Tribunal criminal proceedings, information or evidence related to a crime within the jurisdiction of the Special Tribunal’, thereby giving the national Prosecutor General the power to choose which files, suspects, and bodies of evidence are transmitted to the Tribunal’s Office of the Prosecutor for further investigation and potential indictment. In practice, this referral mechanism effectively makes the Ukrainian Prosecutor General the primary funnel through which the Special Tribunal’s caseload is populated, while the Tribunal’s Prosecutor retains the authority to assess on an independent, international‑law‑based standard whether the materials substantiate ‘reasonable grounds to believe’ that a person committed the crime of aggression and whether to proceed with an investigation or prosecution. 

Could the Tribunal’s Prosecutor open investigations proprio motu? There is considerably ambiguity about it, in the Statute.[66] The Statute of the Special Tribunal can plausibly be interpreted as precluding proprio motu investigations by the Tribunal’s Prosecutor because Articles 23 and 24 frame the Prosecutor’s jurisdiction in a way that appears to tie the initiation of proceedings to the prior action of Ukraine, rather than granting an autonomous power (contrary to Article 15 of the Rome Statute, for example). The arrangement enhances Ukrainian ownership of the justice process but also raising concerns about politicisation or selective referrals, since the Tribunal’s Prosecutor generally cannot initiate investigations proprio motu without prior national referral, so the Ukrainian Prosecutor General’s choices regarding priority cases and evidence sharing directly shape the scope and fairness of accountability at the international level.

4.   The Tribunal and European law: selected issues

4.1.  The Council of Europe and EU law

The establishment of the Special Tribunal within the framework of the Council of Europe is constitutionally significant for the European Union not only because of the EU’s involvement in its creation, but also because of the dense entanglement between the two European legal orders: both the Council of Europe and the EU protect fundamental rights through distinct yet closely interconnected systems.[67]The Special Tribunal is not a human rights court. It has no autonomous mandate to develop a catalogue of fundamental rights, and it is not empowered to review national measures for compliance with rights as such. But, it cannot avoid interpreting the fundamental rights protected under its statute (some of which are discussed in Section 3.3) when it applies them: right to a fair trial, ne bis in idem, presumption of innocence, right against self-incrimination, and so on. That interpretation has to come from somewhere. It shall be recalled that the applicable law is the Statute itself and rules of procedures (to be adopted); in second place, ‘applicable treaties, customary international law and general principles of law when necessary to ensure compliance with accepted standards of international criminal law’;[68] failing that, substantive Ukrainian criminal law. Depending on what the relevant applicable treaties are (on which see also discussion in Section, 4.2), and/or on the basis of Article 31 of the Vienna Convention on the law of Treaties, the Tribunal may refer to ECHR law or to EU law. International criminal courts often refer to ECtHR case law, for example on fair trial.[69]

The Tribunal could not, plausibly, adopt an understanding of fundamental rights that would fall below ECHR standards, because it may expose Ukraine and cooperating States to liability under that Convention if national courts are required to enforce a judgment of the Tribunal. Nor can it diverge from EU Charter-level protection either, because EU Member States would then face a collision between cooperation obligations and EU constitutional requirements. In practice, a national court of a Council of Member State – such as Ukraine – or EU Member States might refuse to give effect to a decision of the Tribunal if it found it was adopted in violation of a fundamental rights. This scenario shows the potential for conflicts of loyalty (compliance with the Tribunal vs other international commitments). 

4.2.  A tension with the autonomy of EU law?

When it comes to potential conflict with EU law, at issue is the principle of autonomy, a cornerstone of the Union’s unique constitutional architecture, which may be on a trajectory of conflict with provisions within the Tribunal’s Statute. Autonomy posits the Union legal order as a self-referential and complete system, distinct from both public international law and the domestic law of the Member States.[70] It entails the exclusive jurisdiction of the Court of Justice of the European Union (CJEU) to deliver the definitive interpretation of Union law binding on EU institutions.[71] The Special Tribunal’s mandate, specifically its power to apply international treaties (Article 3b Statute), creates a potential for collision with this exclusive jurisdiction – a collision that meticulously crafted agreements, such as the EU-Canada Comprehensive Economic and Trade Agreement (CETA), have been carefully engineered to preclude.[72]

The autonomy of the Union legal is a constitutional imperative essential for the functioning of a system designed to bind sovereign States into an ‘ever closer union’.[73] Its doctrinal foundations were laid by the CJEU in a series of seminal rulings,[74] in which the Court held that “the founding treaties of the EU, unlike ordinary international treaties, established a new legal order, possessing its own institutions, for the benefit of which the Member States thereof have limited their sovereign rights, in ever wider fields, and the subjects of which comprise not only those States but also their nationals.[75]

To safeguard these specific characteristics, the Treaties have established a sophisticated judicial architecture with the CJEU at its apex, charged under Article 19 TEU with ensuring that ‘in the interpretation and application of the Treaties the law is observed’.[76]This system is constitutionally entrenched by Article 344 TFEU, a pactum de non petendo whereby Member States undertake not to submit a dispute concerning the interpretation or application of the Treaties to any method of settlement other than those provided for therein. This provision enshrines the Court’s jurisdictional monopoly. The CJEU has guarded this monopoly zealously, most notably in Opinion 2/13 concerning the EU’s accession to the ECHR, where it held the draft agreement to be incompatible with the Treaties, inter alia, because it failed to preclude the European Court of Human Rights from ruling on disputes between Member States or between a Member State and the Union concerning the application of the ECHR within the scope of Union law. In later judgments, such as Achmea and Opinion 1/17, the Court clarified that the autonomy of EU law is adversely affected whenever EU institutions would be bound by an interpretation of EU law delivered by a court that is outside the EU judicial system.[77]

It is against this constitutional backdrop that the Statute of the Special Tribunal must be assessed. Admittedly, the potential conflict with EU law should not be overemphasised, but it is there nonetheless. One can envisage a scenario where a defendant before the Tribunal argues that the act of aggression was a response to unlawful economic coercion by the EU, specifically citing the sanctions regime imposed since 2014. The defence might contend that these sanctions violated an international agreement binding upon the Union, such as a Partnership and Cooperation Agreement.[78] The Tribunal, empowered under Article 3(b) of its Statute to apply ‘applicable treaties ... and general principles of law’, would be compelled to assess this defence. In so doing, it would have to interpret the provisions of the EU-Russia agreement and rule on the legality of the Union’s sanctions. Such a judicial exercise would create an irreconcilable conflict with the principle of autonomy, if EU courts or courts in an EU Member State were asked (as they might) to enforce the judicial decision of the tribunal which has declared – unlikely as this may be – EU law invalid. International agreements concluded by the Union are an integral part of the Union legal order,[79] and sanctions adopted under the Common Foreign and Security Policy are acts of Union law. Consequently, by adjudicating on the validity of those sanctions, the Special Tribunal would be usurping the interpretative function that Articles 19 TEU and 344 TFEU reserve exclusively for the CJEU. 

It is the mere potential of such an interpretation that poses problems to the autonomy of EU law as interpreted by the Court of Justice of the EU. Consider, by contrast, the investor-State dispute settlement (ISDS) mechanism in the Canada-EU Trade Agreement, which the Court scrutinised in Opinion 1/17. The CJEU found the CETA mechanism compatible with EU law precisely because it contained a series of robust safeguards conspicuously absent from the Special Tribunal’s Statute: crucially, CETA expressly denies its tribunals the power to rule on the legality of a measure under the domestic law of the parties. Instead, a CETA tribunal must treat Union law as a ‘matter of fact’ and is bound to ‘follow the prevailing interpretation’ given to that law by the competent courts, namely the CJEU.[80] These safeguards ensure that the CETA ISDS mechanism cannot interfere with the CJEU’s role as the ultimate arbiter of Union law.

Article 3(b) Statute, instead, confers a broad mandate to apply treaties without the limitations that were central to the Court’s acceptance of the validity of CETA in Opinion 1/17. The Tribunal agreement and its statutes are not EU acts, so cannot be challenged directly before the CJEU, but are binding on all its Member States. The issue would manifest at enforcement level, in circumstances where a court of a Member State is asked to enforce a judgment of the Tribunal. Such a domestic court may (have to) involve the Court of Justice of the EU through a preliminary reference.

4.3   Relationship with the ICC and the development of international law

As the one of its main political and financial stakeholders, the EU had an interest in preserving the coherence of the juridical architecture established by the ICC. The concern, articulated by certain scholars and diplomats, was that a proliferation of ad hoctribunals could dilute the political capital, financial resources, and precedential authority underpinning the universalist aspirations of the ICC.[81] The EU had an interest in making the Special Tribunal complementary (not rival) to the ICC. This was achieved through the Tribunal’s circumscribed jurisdiction and through integrated evidence-gathering frameworks. Article 31 of the Statute imposes an obligation upon the Tribunal to cooperate with national authorities, including those participating in the International Centre for the Prosecution of the Crime of Aggression. The ICPA, situated within the EU Agency for Criminal Justice Cooperation (Eurojust), functions as a fulcrum for investigative coordination.[82] Evidence collated by the Joint Investigation Team and archived within Eurojust’s Core International Crimes Evidence Database is rendered accessible to the Special Tribunal.

The Union’s engagement in the creation of the Special Tribunal is a contribution to the progressive development of international law itself (constitutionally mandated by Article 3(5) TEU). The EU is increasingly regarded as an actor whose practice informs the formation and identification of customary international law.[83] It has been observed, for instance, that the jurisprudence of the CJEU concerning the scope of EU regulations has indirectly influenced the manner in which Member State courts interpret the public international law doctrine of State immunity.[84] In cases like RINA, the CJEU’s teleological interpretation of Union law contributed to a narrowing of the immunity afforded to private entities exercising public functions, thereby shaping the trajectory of State practice.[85]

By assuming a leading role in the drafting and promotion of the Tribunal’s Statute, the EU and its Member States generate significant State and International Organisation practice on some of the most controversial questions of international criminal law. Furthermore, the Statute adopts an unambiguous position on the classic antinomy between peace and justice. Article 4(3) of the Statute provides that ‘An amnesty granted to any person falling within the jurisdiction of the Special Tribunal [...] shall not be a bar to prosecution’. While amnesties may secure peace after a conflict, they do so at the expense of accountability for the perpetrators of the gravest international crimes. In explicitly precluding amnesties as a defence, the Statute’s drafters have made a decisive choice. 

Article 48 Statute provides for cooperation between the Special Tribunal and the EU. This article creates the legal basis for the conclusion of agreements to facilitate such cooperation, with a particular focus on the exchange of information. The instrumental importance of this provision can scarcely be overstated, as the EU and its Member States are repositories of a vast corpus of information pertinent to the crime of aggression.

5.   Conclusion

The establishment of the Special Tribunal for the Crime of Aggression against Ukraine is a landmark in the evolution of international criminal justice and a defining moment in the European Union’s role as a global actor committed to a rules-based system. 

The design of the Tribunal has some noteworthy features that are likely to determine its success or failure depending on how the relevant actors interpret their role in practice. It combines international judges with a decisive gatekeeping role for the Ukrainian Prosecutor General. The rejection of functional immunity aligns the Tribunal with an accountability-oriented reading of international criminal law, and the temporary preservation of personal immunities for the highest State officials reflects a cautious deference to State sovereignty. The fact that most trials are likely to be in absentia is perhaps a serious flaw in the credibility of the tribunal, but the institution would be unlikely to be able to operate at all otherwise. 

An aspect of particular importance from the prism of EU law is the potential for judgments of the Tribunal to adversely affect the autonomy of EU law, by binding EU institutions to an interpretation of EU law delivered by a Tribunal that is outside the EU judicial system. This is merely potential, but it ought to be mentioned nonetheless. 

It was noted, in particular, that the Tribunal’s embeddedness in the Council of Europe legal framework and in the European legal space places its proceedings under the shadow of ECHR (and EU fundamental rights) standards. This relationship is likely to act as both a constraint and a source of legitimacy, compelling the Tribunal to interpret its Statute consistently with Convention (and EU) case law.