(Editor’s note: This article is part of Just Security’s Symposium, International Law in the Face of Russia’s Aggression in Ukraine: The View from Lviv.)

In the years since Russia began its full-scale invasion of Ukraine in February 2022, the international community has reacted to the aggression with a variety of legal responses. From supporting domestic prosecutions to pushing efforts to establish a new tribunal for the crime of aggression, Ukraine may represent a unique case of the full use of available mechanisms within the existing system of international criminal justice. During an ongoing conflict, this “accountability ecosystem” has responded to crimes in diverse and innovative ways, employing existing criminal law frameworks on the national, transnational, and international levels to pursue different pathways to justice.

While most of these developments are praiseworthy, it is also important to recall the limitations of criminal justice, both in its national and international components. The history of international criminal justice is, first and foremost, one of protracted struggles by multiple actors, starting with victims and affected communities, to secure accountability for the worst imaginable crimes. But it is also a history of misplaced assumptions, excessive expectations and, ultimately, frustrations. More often than not, even the combined, sustained, and good-faith efforts by national, regional, and international institutions lead only to a modicum of accountability, leaving large portions of those who suffered the crimes without any meaningful redress (or a largely symbolic one).

These facts should neither be used to indict the entire system, nor render us cynical about it. But experience does urge caution, and the need to acknowledge the potential and limits of our justice systems, as well as locating criminal justice within the broader set of complementary avenues towards justice, accountability, and redress for the victims in Ukraine and elsewhere. As this post will explain, each pathway to justice has inherent limitations and challenges, and can only deliver a measure of accountability. Keeping these limitations in mind from the outset may enable us to approach situations of mass violations of international humanitarian law and human rights law with a wider lens and find synergies and complementarities in our responses.

Ukrainian Prosecutions

As the territorial State, Ukraine takes the lion’s share of the accountability work. The responsibility falls, first and foremost, on the shoulders of Ukraine’s Office of the Prosecutor General (OPG), which had to become, overnight, a war crimes-prosecuting machine. Prior to the current hostilities, OPG had a small war crimes unit focused on Crimea-related war crimes. The scale of the crimes committed during the wave of armed violence starting in February 2022, however, clearly surpassed the capacity of that unit and required an effort in institutional re-engineering of OPG, which involved the conversion of prosecutors with limited prior experience in the field into war crimes prosecutors almost overnight. At the time of writing this piece, OPG is investigating more than 120,000 incidents involving potential war crimes. Some questions have arisen as to the methods used for mapping and counting cases, but even if corrective action – such as discarding duplicates and piecing together separate dossiers, which should be viewed as forming a single case – reduces the actual number of cases somewhat, the sheer scale of cases would still be overwhelming, and would pose major challenges to even the best equipped national prosecutorial bodies. To OPG’s credit, none of this has happened: the office overcame the initial shock, adjusted its methods to manage the workload, and effectively harnessed international assistance to acquire the necessary expertise. To date, Ukrainian prosecutors have identified 695 suspects (and secured 83 convictions for war crimes under Article 438 of the Criminal Code) before the country’s national courts.

Among the forms of international support is the Atrocity Crimes Advisory Group, or ACA, an international consortium comprising 5 implementing partners – Georgetown University, the European Union Advisory Mission to Ukraine, Global Rights Compliance, the International Development Law Organization, and Pravo Justice. ACA is funded by the United States, the EU, and the United Kingdom, with the mission of providing technical support and advice to the OPG in the investigation and prosecution of war crimes. This is, to my knowledge, an unprecedented case of direct technical support by an international consortium to a national prosecuting office. And it has borne some fruit: after two years of collaboration, the OPG’s expertise is heightened, policies and strategies are being put in place, international expert support, including forensic teams, has been pouring in, and, as said, many cases have been brought forward.

Unsurprisingly, a number of challenges remain. These include developing criteria for prioritization of cases, moving up the chain of command for suspects in the next generation of cases, optimizing the use of existing resources, digitalizing internal processes, including registration of evidence, and modifying or adjusting dated procedural mechanisms, among others.

A significant problem in the mid- and long-term is sustainability of the effort. The scale and length of this conflict could have easily justified a special international tribunal, in the model of those established for the Former Yugoslavia and Rwanda. However, the current model of international criminal justice rests more in a division of labor between national jurisdictions and the International Criminal Court (ICC), with a few exceptions (e.g. Special Criminal Court for the Central African Republic). The only ongoing discussion involving an additional international jurisdiction is confined to the crime of aggression, where, due to the combined effect of the jurisdictional loopholes in the ICC Statute and the international law principles on immunity, at least personal immunities of the highest echelon of power, there is a noticeable impunity gap.

The national judicial system in Ukraine is therefore the main entity responding to the vast numbers of criminal cases involving international crimes, alongside “ordinary” domestic crimes, which, after a sharp decline at the beginning of the conflict, are now slowly on the rise. These include fraud, drug smuggling, and peripheral crimes linked to the conflict, such as human and arms trafficking. As a consequence, the OPG is caught between two waves: an increase in ordinary crimes and massive demands created by the war crimes workload. The development of a sustainable model, capable of effectively dealing with the war crimes cases over a prolonged period, is therefore vitally important. In this sense, Ukraine and international donors can learn from comparable national experiences where States have established specific judicial mechanisms tasked with processing the cases emanating from an armed conflict, including after cessation of hostilities, such as the War Crimes Chamber of the Court of Bosnia and Herzegovina.

Third States and Universal Jurisdiction

The second forum for accountability is third States exercising jurisdictions through use of universal jurisdiction or some other point of connection enabling extraterritorial exercise of criminal jurisdiction, such as passive personality (jurisdiction flowing from the nationality of the victim). Here again, there are important innovations, chiefly the formation of the Joint Investigative Team (JIT) – a consortium initially formed by Ukraine, Lithuania, and Poland, and later joined by Estonia, Latvia, Slovakia, and Romania, under the auspices of Eurojust, the EU’s Agency for Criminal Justice Cooperation.

The ICC Office of the Prosecutor (OTP) and Europol subsequently joined, further increasing international cooperation efforts. The creation of the JIT was accompanied by an expansion of Eurojust’s functions, now adding a critical role as a evidence repository through the creation of the Core International Crimes Evidence Database where evidence is stored and analyzed for the benefit of all States joining efforts under the JIT umbrella. We also have the new International Centre for the Prosecution of the Crime of Aggression in Ukraine (ICPA), a prosecutorial hub also hosted by Eurojust, where prosecutors seconded by various countries work together and exchange evidence with a view to preparing future cases of aggression that may be prosecuted nationally or internationally. The ICPA is another creative response to bridge the lack of an existing mechanism, national or international, capable of addressing the highest levels of political responsibility for the crime of aggression against Ukraine, given the jurisdictional limits of the ICC and impediments that the law on immunities poses before national courts. To date, around 20 States are currently engaged in investigative activities related to the Ukrainian armed conflict, and two of them (the United States and Lithuania) have issued charging documents.

While these initiatives are certainly both meaningful and promising, extraterritorial domestic prosecutions based on international crimes have proved fraught for decades. These include: (a) inadequate or incomplete national legislation (e.g. no exception to statutes of limitations, defective codification of international crimes, lack of adequate modes of liability or of command responsibility, and approaches that fail to center the victims of sexual or gender-based crimes); (b) lack of adequate procedural tools (e.g. bureaucratic procedures and requirements blocking access to justice to victims and survivors, no effective protection measures for victims and witnesses, and dated evidentiary requirements, among others); (c) lack of expertise in the investigation and prosecution of war crimes and crimes against humanity; and (d) lack of flexible and efficient international cooperation mechanisms.

All these shortcomings can be dealt with. For instance, the JIT was created precisely to improve cooperation and evidence-sharing between the different investigating States. There is also experience to draw on: a recent study by the International Center for Transitional Justice showed that those countries which had established a specialized unit for the investigation and prosecution of war crimes fared much better than those which left atrocity crimes to staff without such expertise. However, practice also shows that specialized units frequently face serious resource limitations and become overstretched, and their output unavoidably suffers as a result. For instance, some national investigative war crimes units have been merged with units in charge of terrorism-related investigations, which has led to the latter activities becoming prioritized in practice.

On top of that, national war crimes units frequently lack the type of ancillary infrastructure present in international criminal jurisdictions – such as operational planning units, language support staff, ground logistics including safe transportation and accommodation, among others – which has become essential for transnational investigative activities. In addition, in States where national or federal prosecutors work in parallel with regional ones, developing expertise at a central level may bring limited benefits if a similar process is not undertaken at the regional level, too. In terms of international cooperation, the recently concluded Lubjliana-The Hague Convention, and the many innovations it includes for the purposes of bolstering State-to-State cooperation in the investigation and prosecution of international crimes, certainly constitutes a critical step towards much more coordinated and efficient horizontal cooperation, but the Convention is still in the infancy of its operational life, with a few dozen signatories to date. Finally, while national jurisdictions tend to be effective in the prosecution of perpetrators who happen to be located on their territory, they face even greater challenges when it comes to arresting suspects abroad, as a result of a much less dynamic system of international cooperation and procedural obstacles, which may not apply to international criminal jurisdictions (such as immunities).

Nothing here should cause a loss of faith in the promise of accountability held by national jurisdictions. On the contrary, not only do they remain the first line of response vis-à-vis the commission of atrocity crimes; they have also evolved significantly in this regard in the past 20 years, including with respect to universal jurisdiction. For instance, TRIAL International reported cases or investigations against 217 suspects based on universal jurisdiction during 2023, including 36 new cases. But it is important to recognize the challenges and limitations and to respond to them, and to manage expectations accordingly.

International Criminal Court(s)

Finally, we have the international criminal responses to the atrocity crimes committed in Ukraine, which, until such time as an international criminal tribunal for the crime of aggression is created (assuming it eventually is), remains confined to the ICC.

Almost from the outset of the conflict, or at least as it became apparent that serious International Humanitarian Law (IHL) violations were being committed, there was a demand for robust ICC engagement. This was reflected by the unprecedented number of States (43 in total) referring the situation in Ukraine to the ICC Prosecutor, in an effort to allow OTP to directly open an investigation without the need to seek authorization first from a Pre-trial Chamber, as mandated by Article 15 of the Rome Statute for certain types of investigations. This responsibility landed on an institution that was already severely overstretched, working across multiple situations spanning four continents and involving different challenges. However, through an innovative combination of in-house resources with voluntary contributions and seconded personnel, the ICC has produced very significant results in a very short period of time, with four arrest warrants publicly announced against high-level suspects (including the very President of the Russian Federation). And since arrest warrants are only the tip of the iceberg when it comes to prosecutorial activities, it would not be surprising if other lines of inquiry, and with them new potential warrants, are underway.

Here, too, questions of sustainability arise. The ICC cannot become the international criminal court for Ukraine without unavoidably adversely impacting on the progress of other situations or cases. In this sense, the results shown to date in the Ukraine situation are surprisingly positive, compared with the much more meager results in other situations which have been active for longer. This inevitably raised questions as to internal distribution of resources and prioritization, and even allegations of double standards, in particular in relation to the initial and for some, more muted, reaction of the OTP to the situation in Gaza. However, as has recently become clear, the OTP was fully active on this latter dossier and has requested arrest warrants against top leaders on both sides of the conflict, including the Israeli Prime Minister, putting an end to weeks of speculation. The accumulation of this complex active investigation underscores questions as to the implications for the sustainability of the OTP’s efforts in Ukraine. And these are only two of the many active situations from a wider spectrum where demands will continue to be heard and questions asked.

Transitional Justice?

The final line of response for justice in Ukraine remains, for now, purely hypothetical: the possible use of transitional justice mechanisms to deal with at least some of the crimes committed during the armed conflict. In its recent report, the U.N. Independent International Commission of Inquiry on Ukraine emphasized the significance of non-criminal dimensions of accountability, such as truth, reparations, and guarantees of non-recurrence. These are forms of justice and accountability that Ukraine should explore, and is already implementing in the context of conflict-related sexual violence. Here too there are challenges. The particular nature of the armed conflict in Ukraine may not be compatible with combinations of criminal and restorative justice like Colombia’s innovative Special Jurisdiction for Peace. It is one thing to develop a transitional justice mechanism in a peace process involving local actors seeking to end a non-international armed conflict, which is geared towards internal healing and restoring the social fabric ruptured by the armed violence; it is a very different one to address serious violations by a foreign power in the context of an ongoing international conflict with no clear end in sight. The views of the affected communities, unsurprisingly, reflect this: according to a recent survey, 75 percent of respondents consider that justice cannot be achieved without the arrest and trial of those responsible for the attack on Ukraine and the ensuing war crimes.

Nonetheless, the particular features of the Ukraine armed conflict and the demands of those affected by the crimes does not preclude a role for transitional justice mechanisms. While they may not substitute for criminal processes, which will be required to address the most serious international crimes allegedly committed by Russian forces, there may be scope for such mechanisms and processes for other crimes related to the conflict, including alleged instances of collaboration by Ukrainian nationals with Russian troops in occupied territories. These are increasingly being widely prosecuted in Ukraine, raising questions as to the scope and role of criminal law. Indeed, exploring pathways to justice other than criminal prosecutions for at least some of these cases may ultimately be a better investment in a future and united post-conflict Ukraine than prosecuting each in every instance of alleged collaboration with the enemy.

The Ukraine situation is making full use of the justice toolkit, in some cases in a highly creative manner. While ultimately the success of the exercise will be assessed on the basis of its outcome, in particular from the perspective of victims and survivors, it must be borne in mind that the duty to investigate and prosecute international crimes is one of means, not of result. In this sense, the combined and robust reaction from national, regional, and international institutions should be hailed as a much-welcomed reaffirmation of the commitment to justice and the demand of “never again.”

Fabricio Guariglia is Director of The Hague Branch Office of the International Development Law Organization (IDLO). He is former Director of Prosecutions in the Office of the Prosecutor of the International Criminal Court. The views expressed herein are solely the author’s and should not be attributed to IDLO. The author thanks Helen Duffy and Tamar Tomashvili for their helpful comments and suggestions.

IMAGE: Ukrainian President Volodymyr Zelenskyy speaks during a joint press conference with President of Finland Alexander Stubb on April 3, 2024, in Kyiv, Ukraine. (Photo by Viktor Kovalchuk/Global Images Ukraine via Getty Images)