This month marks the fourth anniversary of Russia’s full-scale invasion of Ukraine. This unlawful war represents the most egregious violation of international law in Europe since the Second World War. It is a textbook example of the crime of aggression and demands accountability.
Establishing a credible mechanism of accountability has been difficult, but the international community has remained steadfast in its determination to bring Russian leaders to justice.
After more than three years of sustained effort, the foundational agreement formally establishing the Special Tribunal for the Crime of Aggression against Ukraine (STCA) was signed on June 25, 2025, in Strasbourg, France, by Ukraine and the Council of Europe, a 46-member intergovernmental organization aiming to advance human rights, democracy and the rule of law. Crucially, the STCA is not an externally imposed mechanism. It is the result of sustained Ukrainian leadership — legal, diplomatic, and political — supported by partners but driven by those who best understand the crime, its context, and its victims.
The STCA represents a decisive step toward closing a longstanding gap in international criminal accountability. While the crime of aggression is a crime under customary international law and is prohibited under Article 2(4) of the United Nations Charter, the International Criminal Court’s (ICC) jurisdiction over the crime of aggression is uniquely restricted. The Court may exercise jurisdiction if the U.N. Security Council refers a situation, a scenario unlikely in the case of Russia, given its veto as a permanent member. Otherwise, the Court may exercise jurisdiction only where both the aggressor and victim states are Parties to the Rome Statute and have accepted the Court’s jurisdiction over the crime of aggression, and where no opt-out declaration has been made. As Russia is not a State Party, the ICC lacks jurisdiction over the crime of aggression against Ukraine.
The STCA is not merely a response to Russia’s aggression. It is a Ukrainian contribution to the architecture of international criminal justice. Beyond Ukraine, the STCA agreement has broader significance: it reaffirms that the prohibition on the use of force is a cornerstone of the international legal order, strengthens deterrence against future wars of aggression, and demonstrates that even the most senior political and military leaders are not beyond the reach of the law.
Accession Process Begins
The accession process has now commenced, allowing states to join an Enlarged Partial Agreement (EPA) to govern the STCA. Under Council of Europe regulations, a minimum of 16 member states is required for the EPA to enter into force. In the case of the STCA, however, it is estimated that 25 to 30 states will be necessary to demonstrate its political legitimacy and financial sustainability. On Feb. 11, the Estonian Parliament approved legislation to join the EPA, making Estonia the first country to do so. It is also anticipated that states beyond the Council of Europe will participate, underscoring the STCA’s broad geographical and political support.
Two of the most challenging aspects of establishing the STCA are determining the overall cost and ensuring that implementation proceeds expeditiously. The nature of its task, particularly its focus on Russia’s leadership, brings unique risks to the STCA. Consequently, robust physical security, data protection, witness protection, detention facilities, and a dedicated Tribunal building will be needed. These requirements significantly increase the overall cost. Thus, states are understandably seeking further clarification of this issue as they contemplate committing to the EPA.
At the same time, the STCA must become operational without delay to safeguard its credibility and prevent political erosion or attempts to undermine or obstruct its establishment. So it is essential that the process of establishing the STCA receives sustained political and financial support as early as possible.
Phases of Implementation
In response to these challenges, during the meeting of STCA Working Party in Strasbourg, Ukraine proposed an innovative approach. The STCA can be implemented in three phases: (“0”) an advance team; (“1”) a skeleton tribunal; and (“2”) the full operational tribunal.
Phase 0 will begin with a small advance team working in both Strasbourg and the Netherlands for roughly 1½ to 2 years before fully relocating to the Netherlands. They will develop the institutional architecture of the STCA, including internal rules and procedures, staffing frameworks, and security requirements, and find premises in The Hague for the skeleton tribunal phase. In short, Phase 0 transforms the STCA from a formal legal agreement into a functioning institutional blueprint. The European Union has allocated €10 million (US$11.9 million) to support this phase for 2026-2027.
Phase 1 will continue the project in the Netherlands by establishing a “skeleton tribunal.” This phase will transition from institutional design to functionality and will expand upon the foundational work of Phase 0 by recruiting and appointing key personnel, such as judges, establishing the registry, implementing operational systems, and setting prosecutorial priorities. The skeleton tribunal will have legal standing and enter into a host country agreement.
Equally important, Phase 1 builds institutional credibility. By demonstrating tangible operational capacity, the skeleton tribunal reinforces political confidence among participating states, encourages further accessions to the EPA, and strengthens donor commitment, supported by annual membership contributions from participating states.
Together, Phases 0 and 1 are expected to take several years. This timeline is comparable to the establishment of the ICTY and the ICTR, both of which required multiple years between their initial authorization and the commencement of trials.
In the final phase, the STCA will become fully operational, with courtrooms, detention facilities, secure transport arrangements, and permanent premises. Indictments, the issuance of arrest warrants, and trials in absentia will be part of this final phase.
Resilience to Political Pressure
An international criminal proceeding of this complexity needs to be resilient against political pressure. The phased model is intended to ensure sufficient political will and financial support so that the tribunal will succeed in upholding the foundations of international law. However, the establishment of the STCA is no longer a question of “if,” but of “how fast” and “how robust.” Each completed phase reduces political reversibility and increases legal inevitability.
To ensure the STCA’s success, sustained political engagement and concrete diplomatic action are essential. Ukraine, together with legal advocacy organizations such as the International Bar Association, is actively engaging governments to support the rapid adoption of the EPA, either as Full or Associate members, to secure meaningful accountability for the war against Ukraine. This approach shifts the narrative from the resource commitments required to establish the Tribunal to the far greater cost of non-accountability, positioning the STCA as a strategic investment in global security. If the crime of aggression is not prosecuted now, it will be permanently normalized. The stakes could not be higher.
– Iryna Mudra, Ambassador Anton Korynevych and Mark Ellis, Published courtesy of Lawfare.
