Rethinking evidence in war crimes investigations: covertly obtained material

Ukraine is investigating/prosecuting aggression, war crimes, crimes against humanity, and genocide while a full-scale international armed conflict is ongoing. Few domestic systems have attempted accountability for mass atrocities at this scale and under such conditions. Ukrainian prosecutors operate with restricted access to occupied territories, limited access to insider witnesses or suspects, and little prospect of obtaining internal Russian military documentation or command communications.

In these circumstances, covert information originating from Ukrainian military, security, and intelligence bodies becomes indispensable. It may derive from a variety of covert actions and may include intercepted communications, the examination of "trophy" documents abandoned by Russian forces during their retreat and later discovered in liberated areas, insider information, and other forms of surveillance and battlefiled intelligence.

For example, intercepted conversations between commanders and their subordinates frequently reveal not only the operational and battlefield plans, but also command orders or discussions related to the establishment of occupying authorities in the occupied territories and their actions towards civilians living there. In some instances, such conversations may constitute direct proof of orders to commit, or of the commission of killings, unlawful detention, tortures, and pillage. They may confirm the location of particular units, their headquarters and checkpoints, and help establish the identity of perpetrators, their roles, as well as commander's place in the chain of command and the overall atmosphere within the unit.

All of this may be crucial for supporting war crimes investigations, as operational context, unit presence in a particular area, command structures, and communication and decision-making patterns are precisely the elements required to establish linkage and the responsibility of higher echelons of the Russian command. The importance of such insights becomes particularly evident when direct linkage evidence is lacking. In such cases, the prosecution may need to demonstrate a commander's knowledge of the actions of subordinates or establish a link between their indirect orders and the crimes committed.

As reflected in the practice of international courts and tribunals, the importance of this type of confidential material for investigations into international crimes is not unique to Ukraine. Yet using this material as evidence always raises procedural and practical challenges, including in Ukraine.

Definition of Covert Material and Evidentiary Challenges

Battlefield interceptions, Russian military documents, and other covert sources revealing the broader military context in war-crimes investigations are often generated by law enforcement, security, military, and intelligence bodies through both investigative measures and covert activities. There is no single legal term that encompasses all such material. For ease of discussion, it is therefore useful to refer descriptively to covert material. This is not a statutory category. It simply denotes information covertly obtained by the mentioned authorities and relevant and probative of responsibility for international crimes.

Despite the significance of such material, its use as evidence gives rise to three distinct challenges:

• with respect to intelligence material, the absence of a clear legal framework governing its use as evidence;
• with respect to other covert materials, the practical difficulties of ensuring a chain of custody in wartime conditions; and
• the broader challenge of source verification, stemming from the nature of covert material.

First: The Legal Gap Around Intelligence

In Ukrainian law, "intelligence" has a specific and narrow meaning. It refers to information relating to foreign actors or to the national security and defence of Ukraine that cannot be obtained through public or official channels. It is classified according to its sources and methods.

Unlike operative and counterintelligence information, intelligence is not designed to function as courtroom evidence. The Criminal Procedural Code does not regulate how such intelligence may be transformed into admissible proof, nor does it establish a structured framework governing cooperation between intelligence bodies and prosecutors once intelligence becomes relevant to a criminal case. In practice, intelligence bodies may simply decline to disclose information necessary for criminal investigations.

As a result, intelligence could be used to guide investigations, identify suspects, and shape prosecutorial strategy – but it cannot easily enter the courtroom as evidence.

Second: Wartime Chain-of-Custody Realities

A different problem concerns covert material obtained during the earliest and most chaotic stages of the full-scale invasion. Command communications or other forms of covert information were usually collected for battlefield purposes rather than evidentiary once, despite later becoming crucial for war crimes investigations.

For example, in the first month of invasion, various Ukrainian security and military bodies intercepted communications of Russian military personnel and commanders in order to identify their locations, movements, troop numbers, plans, and equipment. At that moment, when the survival of Ukraine as a state was at stake, this information was primarily used by the Ukrainian Armed Forces to target Russian units and enable counteroffensive operations and defensive actions. Obviously, in such conditions documentation of origin, metadata, or uninterrupted chains of custody thus could not be always preserved in a manner that corresponds to the standards required for criminal proceedings.

When the chain of custody is compromised and the origin cannot be verified, questions may arise as to the admissibility of such evidence at trial. Even where such evidence is admitted, if documentation is incomplete and such material becomes central to a case, defence challenges concerning authenticity and reliability inevitably gain force.

This is the practical reality of conducting a war and collecting evidence in wartime conditions.

Third: Source Verification When Covert Information Is Central

The most problematic issue arises when security- and military-origin covert information forms the core of a war-crimes prosecution, particularly in cases targeting senior commanders.

Ukrainian courts are not unfamiliar with classified evidence. The difficulty emerges when contextual and linkage evidence depends heavily on information whose original source cannot be fully examined in court. When such material becomes central to the case, the evidentiary burden becomes heavier.

This does not mean such material is automatically inadmissible. It means that when such information carries decisive weight, Ukrainian courts must apply careful and transparent reasoning in assessing reliability.

What International Practice Shows

International criminal jurisprudence provides guidance across such challenges.

The International Criminal Tribunal for the former Yugoslavia relied extensively on military documentation and intercepted communications collected during armed conflict. Admissibility did not depend on whether material originated within ordinary domestic investigative frameworks. Almost all information turned out to be admissible. Instead, judges saw its admission as a question of weight, namely it was examined for authenticity, relevance, reliability, and probative value with a view to attaching probative value to it in the context of the entirity of the evidence. Authenticity was established through testimony, corroboration, and reasoned judicial assessment.

Similarly, the International Criminal Court admits evidence where it is relevant and probative and where its admission does not prejudice the fairness of proceedings. Intelligence- or military-origin material is not automatically excluded; rather, courts evaluate whether the defence have a fair opportuntiy to challenge it to ensure that any resulting convictions are based on sufficient proof.

The European Court of Human Rights has articulated the same principle. The decisive question is whether proceedings as a whole are fair. Even sensitive or irregularly obtained material may be relied upon, provided defence rights are preserved and judicial reasoning explains how reliability was assessed.

Taken together, international practice demonstrates how Ukrainian courts can handle covertly obtained evidence where its authenticity and reliability are challenged. What matters in such cases is a structured assessment of authenticity, corroboration, overall fairness and the weight to be attached to it in the context of the case as a whole.

Rethinking the Role of Covert Material

Ukraine's war-crimes prosecutions must depend on information that traditional investigative measures alone cannot provide. Advancing such cases, particularly those involving senior responsibility, requires greater reliance on covert material. To date, this shift is lacking, and this is one of the key reasons why it remains difficult to achieve progress in command-level cases.

This requires rethinking the role of security- and military-origin covert material by investigators, prosecutors, judges, and security bodies. In practical terms, this may involve:

• Strengthening cooperation between investigative and intelligence bodies, including the development of a workable mechanism for information exchange
• Clarifying the procedural role of intelligence, how it may inform investigations and be converted into evidence as soon as it is no longer operationally significant;
• Recognising the realities of wartime collection and ensuring that courts assess authenticity and reliability with due regard to the conditions under which material was obtained;
• Developing clear judicial reasoning explaining how covert information is evaluated, corroborated, and weighed in war-crimes cases, thus contributing to the development of judicial precedence for the careful admission of this vital evidence;
• Aligning domestic practice with established international standards, and the practice of the European Court of Human Rights in particular, which focus on the overall fairness of trial (and not the excessive focus on discombobulated individual pieces of evidence); and
• Adopting evidentiary guidelines in addition to current procedural laws for the handling of covert material in war crimes investigations.

The objective is to ensure that valuable information stemming from covert actions of security, military, and intelligence bodies, which often becomes central to establishing responsibility at senior levels, does not remain outside formal criminal investigations and is effectively integrated to ensure accountability for international crimes.

This op-ed was co-authored with Kristin Blyckert, international lawyer, Global Rights Compliance