Since the beginning of the Russian invasion of Ukraine, many atrocities are alleged to have been committed, including war crimes and crimes against humanity.[1] The consequent investigations led by the General Prosecutor of Ukraine prove to be challenging given the special nature of the crimes at stake. The fact-finding process for large-scale violations represents a daunting work, and the enormous flow of millions of refugees fleeing the conflict is resulting in the spread of potential witnesses and evidence in different countries. Since the Ukrainian authorities cannot operate alone, different cooperative measures have been adopted at the international and the national level. 

A far-reaching level of inter-state cooperation 

Inter-state cooperation over the investigations on alleged crimes committed in Ukraine translates into measures of mutual legal assistance, which consist of different mechanisms of judicial cooperation by which foreign authorities can help a State’s investigating authorities.[2] In particular, a Joint Investigation Team (JIT) materialised in ‘a legal agreement between competent authorities of two or more States for the purpose of carrying out criminal investigations’ was set up between Ukraine, Poland and Lithuania on 25 March 2022.[3] On 31 May, Estonia, Latvia and Slovakia joined the team, followed by Romania on 13 October. This JIT is the first to include the Office of the Prosecutor of the International Criminal Court (ICC) as a participant.[4] The team works under the supervision of Eurojust, the European agency coordinating the work of competent authorities of EU Member States and some third States to further their cooperation over the investigation and prosecution of transnational and international crimes.[5] The prompt signature of the JIT agreement a month after the beginning of the conflict demonstrates the European Union’s willingness to tackle impunity and achieve accountability.[6]  

To strengthen its actions, the European Parliament and the Council of the European Union amended Eurojust Regulation. The amendment allows for the creation of an ‘automated data management and storage facility’ aimed at ‘preserving, analysing and storing evidence’ as well as ‘enabling the exchange of such evidence with (…) competent national authorities and international judicial authorities’.[7] This new storage capacity was swiftly adopted to be used in the context of the war in Ukraine, however, it is also designed to be at the disposal of any investigation into international crimes involving Eurojust.[8]

Inter-state cooperation with Ukraine is not confined to the JIT. For instance, the European Union, the United Kingdom and the United States created the Atrocity Crimes Advisory Group (ACA) to provide ‘strategic advice and operational assistance’ to Ukrainian authorities.[9] Because the project is grounded on the idea of efficiency, the group connects with other actors involved in the process, including the JIT.[10]

On 28 and 29 November, the Ministers of Justice of the G7 States met with other relevant actors like the Minister of Justice of Ukraine, the Prosecutor of the International Criminal Court or the Prosecutor General of Ukraine. In a Joint Declaration, they reaffirmed their support to the Ukrainian authorities as well as their willingness to improve cross-border cooperation.[11]

The auxiliary support provided by international organisations 

An Independent International Commission of Inquiry on Ukraine was also set up by the UN Human Rights Council in March 2022 to investigate alleged crimes.[12] The Commission engaged in a dialogue with the Ukrainian Government and other relevant international and national actors like the Office of the Prosecutor of the ICC. The information gathered will eventually be submitted to authorities in charge of criminal proceedings.[13]

Other existing entities were called upon to participate in the process. For instance, the EU Advisory Mission for Civilian Security Sector Reform in Ukraine set up in 2014 in order to accompany Ukrainian reforms extended its mandate to assist competent investigative authorities.[14]

Parallel investigations led at different levels

Shortly after the beginning of the conflict, the Office of the Prosecutor of the ICC opened an investigation after the situation had been referred to by 43 States Parties pursuant to Article 14 of the Rome Statute.[15] Although Ukraine is not a State Party to the ICC, the Court can assert jurisdiction on the basis of the ad hoc declaration lodged in 2015 under article 12(3) of the Rome Statute. The jurisdiction of the Court covers alleged war crimes and crimes against humanity perpetrated by Russia on Ukrainian territory since 20 February 2014.[16] However, the Court cannot deal with the alleged crime of aggression because Russia is not a State Party to the Rome Statute and without a referral from the UN Security Council, the Court cannot prosecute aggressions committed by a non-State Party or its nationals.[17] In the process of the investigations, the Office of the Prosecutor exchanges information and evidence with the Ukrainian authorities and States Parties obligated to cooperate under article 86 of the Rome Statute.

At the national level, several States including Poland, Germany, Spain and France have started to collect evidence.[18] Based on extraterritorial heads of jurisdiction like the universality principle or the active personality principle, foreign courts would be able to initiate proceedings for crimes committed in Ukraine.  

Cooperation: the cornerstone of investigations of alleged international crimes 

Russia’s aggression against Ukraine has been condemned by most governments and international organisations.[19] Therefore, their willingness to contribute to the investigative effort reflects the general consensus against the conflict. Whilst some obligations to cooperate can be found in a few topical conventions targeting transnational crimes, such as the UN Convention against Transnational Organized Crimes,[20] no real international provision requires State authorities to comply with a request for legal assistance from another State in case of international crimes like war crimes and crimes against humanity.[21] Although the lack of a legal framework gives a great margin of discretion to national authorities, the collaboration of different actors that have access to useful elements and evidence is paramount. Due to the principle of sovereignty, investigative bodies are prevented from pursuing their activities abroad without the consent of the State concerned.[22] In addition, the exchange of information between the different actors naturally saves time and resources by avoiding the unnecessary overlaps of the same tasks. In practice, it is also a way for victims not to experience re-traumatisation since one testimony can be shared amongst the different authorities involved in the process.[23]

Indeed, the progress of investigations over alleged atrocities can easily be hindered when the investigative State finds no external support. In other words, accountability largely depends on the ‘political will’ of governments to act.[24] 


The development of a multi-level investigation over the atrocities committed in Ukraine provides an encouraging basis for future prosecutions. Eventually, resources spent into the fact-finding process will increase chances to hold perpetrators accountable. The willingness of States and international entities to support the Ukrainian General Prosecutor stands as an exemplary model of international cooperation. However, the bulk of the work is yet to be achieved, and the collaborative work of the different authorities does not resolve the complexity of the collection of evidence on a territory currently used as a battlefield.  

[1] Wolfgang Benedek, Veronika Bílková, Marco Sassòli, ‘Report on violations of International Humanitarian and Human Rights Law, War Crimes and Crimes Against Humanity Committed in Ukraine Since February 2022’ [OSCE, 2022] <; Accessed 11 November 2022.

[2] John A. E. Vervaele, ‘Mutual legal assistance in criminal matters to control (transnational) criminality’in Neil Boister and Robert J. Currie (eds), Routledge Handbook of Transnational Criminal Law  (Routledge, 2014).

[3] ‘Joint Investigations Teams’ (Eurojust) <; accessed 24 November 2022.

[4] ‘Statement by ICC Prosecutor, Karim A.A. Khan QC: Office of the Prosecutor joins national authorities in Joint Investigation Team on international crimes committed in Ukraine’ (ICC, 25 April 2022) <; Accessed 25 November 2022.

[5] Regulation (EU) 2018/1727 of the European Parliament and of the Council of 14 November 2018 on the European Union Agency for Criminal Justice Cooperation (Eurojust), and replacing and repealing Council Decision 2002/187/JHA [2018] OJ L 295/138.

[6] ‘Estonia, Latvia and Slovakia become members of joint investigation team on alleged core crimes in Ukraine’ (Eurojust, 31 May 2022) <; accessed 25 November 2022.

[7] Regulation (EU) 2022/838 of the European Parliament and of the Council of 30 May 2022 amending Regulation (EU) 2018/1727 as regards the preservation, analysis and storage at Eurojust of evidence relating to genocide, crimes against humanity, war crimes and related criminal offences [2022] OJ L 148/1.

[8] ibid.

[9] EEAS Press Team, ‘Ukraine: The European Union, the United States and the United Kingdom establish the Atrocity Crimes Advisory Group (ACA) for Ukraine’ (European Union External Actions, 25 May 2022) <; Accessed 25 November 2022.

[10] ibid.

[11] ‘Berlin Declaration’ (G7 Germany, 29 November 2022) <> Accessed 6 December 2022.

[12] Resolution A/HRC/RES/49/1 adopted by the Human Rights Council on 4 March 2022.

[13] ‘Report of the Independent International Commission of Inquiry on Ukraine’ [2022] Report A/77/533 <; Accessed 25 November 2022.

[14] Press and information team of the Delegation to Ukraine, ‘EUAM Ukraine: Council further amends the mandate to also provide support in the investigation of international crimes’ (EEAS, 13 April 2022) <> Accessed 25 November 2022.

[15] Statement of the ICC Prosecutor, Karim A.A. Khan QC, on the Situation in Ukraine: “I have decided to proceed with opening an investigation”’ (ICC, 28 February 2022) <> Accessed 25 November 2022.

[16] ‘Declaration of the Verkhovna Rada of Ukraine on the Recognition of the Jurisdiction of the ICC by Ukraine over Crimes against Humanity and War Crimes Committed by Senior Officials of the Russian Federation and Leaders of the Terrorist Organizations “DNR” and “LNR”’ [2015].

[17] Article 15 bis of the Rome Statute; Annegret Hartig, ‘Domestic Courts as Gap-Fillers?: Avoiding Impunity for the Commission of the Crime of Aggression against Ukraine’ (Völkerrechtsblog, 12 April 2022) <; Accessed 25 November 2022.

[18] Julia Crawford, Thierry Cruvellier, ‘Ukraine Reponds to Warfare with Lawfare’ (Justice Info, 25 March 2022) <> Accessed 25 November 2022.

[19] See Resolution A/RES/ES-11/1 adopted by the UNGA on 2 March 2022 condemning the aggression against Ukraine.

[20] Article 19 of the UN Convention against Transnational Organized Crime (2020).

[21] Alison Bisset, ‘And then Two Came Along at Once: Inter-State Cooperation on Core Crimes, the ILC and the Group of Core States’ [2020] 20 ICLR 551; Alessandra Annoni, ‘International Cooperation for the Repression of Core Crimes, What Role for the UNTOC?’ [2019] 2-3 BRP 67; Laura M. Olson, ‘Re-enforcing Enforcement in a Specialized Convention on Crimes Against Humanity Inter-State Cooperation, Mutual Legal Assistance, and the Aut Dedere Aut Judicare Obligation’ in Leila Nadya Sadat (ed) Forging a Convention for Crimes Against Humanity (Cambridge University Press, 2011).

[22] John A. E. Vervaele, ‘Mutual legal assistance in criminal matters to control (transnational) criminality’ in Neil Boister, Robert J. Currie (eds) Routledge Handbook of Transnational Criminal Law (Routledge 2014).

[23] ‘Report of the Independent International Commission of Inquiry on Ukraine’ [2022] Report A/77/533 <; Accessed 25 November 2022.

[24] Theodor Meron, ‘Closing the Accountability Gap: Concrete Steps towards Ending Impunity for Atrocity Crimes’ [2018] 112 AJIL 433.

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