The Duty to Investigate War Crimes

by , | Dec 22, 2020

Investigation. Australian Defense Force


On November 19, 2020, a report of the Australian Defence Force’s Inspector-General was released following a four-year investigation into allegations of unlawful killings and mistreatment of non-combatants and persons hors-de-combat in Afghanistan (also known as the Brereton Report). It found credible evidence of numerous violations of the law of armed conflict (LOAC) by Australia’s special forces in that non-international armed conflict.

The release of the report calls attention to the broader issue of a State’s obligation to investigate war crimes. In this article, we briefly examine what the duty entails under both treaty law for States Parties and customary law for all States. We conclude with reflections on the Australian report. But first, for context, some brief details on the report itself.

The Australian Afghanistan Inquiry Report

The investigation concluded that 39 individuals had been unlawfully killed “and a further two were cruelly treated” during 23 incidents involving 25 personnel in 2009, 2010, 2012, and 2013. It asserted the killings, “if accepted by a jury, would be the war crime of murder” and the two other incidents “would be the war crime of cruel treatment.” As a result of the findings, the Inspector-General recommended referral of “36 matters to the Australian Federal Police for criminal investigation.” All 23 incidents and 19 individuals were encompassed in the recommended referrals. The Inspector-General prioritized referral for criminal investigation of those individuals “who have incited, directed, or procured their subordinates to commit war crimes,” rather than those “who may have ‘pulled the trigger.’”

Australia’s inquiry stemmed from “unspecified rumors and allegations of criminal, unlawful or inappropriate conduct, including possible breaches of the Law of Armed Conflict,” by members of Australia’s special forces. These allegations emerged following the conclusion of their operations in 2014. Two years later, the Chief of the Australian Army requested that the Inspector-General conduct the inquiry. During the four-year investigation, over 20,000 documents and 25,000 images were reviewed, and 423 witnesses interviewed.

The New York Times hailed Australia’s four-year investigation and inquiry report as “groundbreaking” and “the first time that a member of the American-led coalition in Afghanistan has so publicly, and at such a large scale, accused its troops of wrongdoing.” Nevertheless, among the many contentious issues surrounding the 19-year conflict in Afghanistan is the supposed failure of parties to the conflict to adequately investigate, and deliver justice for, serious LOAC violations. In fact, the International Criminal Court recently authorized its own investigation into alleged abuses, even though it is effectively a court of last resort pursuant to the principle of complementarity set forth in Article 17 of the Rome Statute. This begs the question of what investigative requirements does LOAC impose on parties to an armed conflict when faced with possible violations?

LOAC Treaty Obligations

Before the two World Wars, the duty to investigate and prosecute war crimes was usually undertaken by individual States through their domestic rules and regulations. The Articles of War and Lieber Code were notable American examples. This is not to say that the concept of international war crimes was non-existent. In fact, the first international war crimes prosecution occurred in 1474 with the trial of Peter von Hagenbach in Austria. However, only after World War II did an international legal requirement for States to act in the face of war crimes emerge. Upon ratification of the 1949 Geneva Conventions, States Parties to those four instruments became bound to three fundamental obligations—to enact domestic legislation required to prosecute alleged war criminals, to search for those accused of committing war crimes, and to try such individuals or turn them over to another State for trial. With 196 Parties, including all members of the United Nations, these obligations are effectively universal.

All breaches of LOAC obligations that are attributable to a State under the law of State responsibility are so-called “internationally wrongful acts” by that State. However, the term “war crime” denotes those LOAC violations that can result in individual criminal responsibility. For example, Article 6 of the 1945 Charter of the International Military Tribunal—the constitutive instrument for the Nuremberg trials—provided that the Tribunal had the “power to try and punish persons who, acting in the interests of the European Axis countries, whether as individuals or as members of organizations,” committed, inter alia, “. . . War Crimes: namely, violations of the laws or customs of war.” Such crimes included, but were “not limited to, murder, ill-treatment or deportation to slave labor or for any other purpose of civilian population of or in occupied territory, murder or ill-treatment of prisoners of war or persons on the seas, killing of hostages, plunder of public or private property, wanton destruction of cities, towns or villages, or devastation not justified by military necessity.”

Article 8 of the Statute of the International Criminal Court similarly outlines a multitude of offenses in both international and non-international armed conflict. Although key States that have been involved in recent armed conflicts such as Iran, Iraq, Israel, Russia, Syria, Ukraine, and the United States are not Party to the Rome Statute, the Article 8 offenses are generally viewed as reflecting war crimes under customary international law. Of particular relevance in the Australian situation, the offenses include murder and cruel treatment during non-international armed conflict.

And under the Geneva Conventions, all “grave breaches” constitute war crimes, even though not all war crimes are grave breaches. Qualification as a “grave breach” results in universal jurisdiction, which allows prosecution by any State, whether involved or not.

The general duty to investigate possible war crimes, as Australia has done, initially derived from nearly identical provisions contained in each of the four Geneva Conventions (GC I, GC II, GC III, GC IV) that required States Party “to search for persons alleged to have committed, or to have ordered to be committed, such grave breaches” and to prosecute them or turn them over to another state for prosecution. Although the text appears to require investigation and prosecution only upon allegation of a “grave breach,” the articles also require States Parties to take “measures necessary for the suppression of all acts contrary to the provisions of the present Convention other than [] grave breaches,” as in the case, for instance, of a violation of Common Article 3 to the Conventions. A duty to investigate is certainly a measure necessary to suppress criminally punishable breaches, regardless of whether or not they are defined as “grave” in the Conventions.

The ICRC’s analysis of the investigate, prosecute, and suppress obligations in the original four Commentaries to the Geneva Conventions supports this interpretation. For instance, it refers to the International Law Commission’s 1954 Draft Code of Offences against the Peace and Security of Mankind, which encompassed all “acts in violation of the law or customs of war,” not just grave breaches. Today, it is clear that the duty to investigate found in the Conventions applies to serious violations thereof that raise the prospect of individual criminal responsibility. The United States and Australia have adopted this approach in the U.S. Department of Defense Law of War Manual (para 18.13), the U.S. Department of Army Field Manual on the Law of Land Warfare (ch 8), and the Australian Defence Law of Armed Conflict Doctrine Publication (para 13.27).

Article 87 of the 1977 Additional Protocol I to the Geneva Conventions supplements the obligation to investigate and prosecute war crimes during international armed conflict by requiring “military commanders . . .  to prevent and, where necessary, to suppress and to report” violations of the Geneva Conventions or the Protocol by anyone under their command or control. It also obliges them “to initiate steps as are necessary to prevent” such violations and “where appropriate, to initiate disciplinary or penal action against violators.” In this context, Protocol I expressly contemplates using the internal structures of armed forces to identify, investigate, and prosecute those responsible for violations. Australia, as a State Party to the Protocol, is subject to these obligations. And while the United States is not a Party to the instrument, it imposes even more extensive requirements on its armed forces (e.g., Department of Defense Law of War Manual (ch 18), Department of Army Field Manual on the Law of Land Warfare (ch 8) and Department of Defense policy).

Notably, the 1977 Additional Protocol II to the Geneva Conventions—applicable to non-international armed conflicts—imposes no duty to investigate alleged war crimes. Nor does Common Article 3 to the Geneva Conventions, the sole provision in those treaties specifically designed for application in non-international armed conflict. This begs the question of whether there is a requirement under customary international law to investigate war crimes during non-international armed conflicts, such as that occurring in Afghanistan.

Customary International Law

International Armed Conflicts

The duty to investigate and prosecute war crimes undoubtedly reflects a customary international law norm during international armed conflict. As observed by the ICRC in Rule 158 of its Customary International Humanitarian Law study, “States must investigate war crimes allegedly committed by their nationals or armed forces, or on their territory, and if appropriate, prosecute the suspects. They must also investigate other war crimes over which they have jurisdiction and, if appropriate, prosecute the suspects.” Note that the International Court of Justice (Nuclear Weapons advisory opinion) and the United Nations (1993 Report of the Secretary-General on Establishment of the ICTY) have characterized the obligations found in the Geneva Conventions as reflecting customary law. There is no reason to exclude the obligation to investigate from the scope of these conclusions. Moreover, Additional Protocol I and many other instruments—including Genocide Convention, Hague Cultural Property Convention and its Second Protocol, Torture Convention, Chemical Weapons Convention, Amended Landmines Protocol, Ottawa Convention on Landmines, Dublin Convention on Cluster Munitions, and the Statute of the International Criminal Court—contain similar obligations. Their inclusion of the obligation to investigate indicates their acknowledgement of its customary nature.

The United Nations has also repeatedly referred to the obligation to investigate and prosecute war crimes. As an example, in 2005 the General Assembly adopted the Basic Principles and Guidelines on the Right to Remedy and Reparation for Victims of Gross Violations of International Human Rights Law and Serious Violations of International Humanitarian Law. It affirmed “the duty to . . . [i]nvestigate [LOAC] violations effectively, promptly, thoroughly and impartially, and, where appropriate, take action against those allegedly responsible . . . .” Most States—including both the United States and Australia—have also passed domestic legislation and imposed a duty on their armed forces to investigate and prosecute war crimes.

Non-International Armed Conflicts

Application of the requirement to investigate in non-international armed conflict is less straight-forward. As noted, neither Additional Protocol II nor Common Article 3 to the Geneva Conventions mentions the obligation. Yet, Rule 158 of the Customary International Humanitarian Law study asserts, with explanation, that the duty applies in such conflicts, an assertion supported by the fact that the treaty instruments cited above in support of a customary rule during international armed conflict are equally applicable in non-international armed conflict.

Moreover, the Rome Statute’s preamble “affirms,” without limitation to international armed conflict, that “the most serious crimes of concern to the international community as a whole must not go unpunished and that their effective prosecution must be ensured by taking measures at the national level and by enhancing international cooperation.” This statement is particularly relevant given that the Statute’s catalogue of war crimes differentiates between international and non-international armed conflicts. Finally, decisions of international tribunals evince support for extending the duty to investigate to non-international armed conflict (e.g., Tadic, paras 111-127).

Content of the Obligation to Investigate

Unfortunately, the relevant provisions of the Geneva Conventions and Additional Protocol I offer only slight guidance on the nature or depth of the investigation that must be conducted into war crimes, or the circumstances that trigger the obligation. However, international human rights law may be looked to by analogy. It imposes an obligation to investigate pursuant to four universal principles—independence, effectiveness, promptness, and impartiality. Regardless of divergent views on the applicability of human rights law in armed conflict (see Department of Defense Law of War Manual para 1.6.3), it is self-evident that compliance with these principles is the foundation of every credible and objective investigation; there is no basis for doubting application of these principles to war crimes investigations.

The four requirements, considered in light of the text and context of the Geneva Conventions and Additional Protocol I, lead to a number of conclusions as to war crimes investigations that have been more fully developed in a study of the matter undertaken by one of the authors. They include:

  • There is no obligation to conduct investigations to uncover LOAC violations. Rather, (1) an allegation of (2) a war crime is the condition precedent to the requirement.
  • The requirement to investigate applies in both international and non-international armed conflict.
  • There is no limitation as to the source of an allegation.
  • If a commander reasonably suspects a war crime has been committed, at minimum, an inquiry must be initiated.
  • Only reasonably credible allegations require investigation.
  • There is no requirement that the identity of the possible offender be known, only that a violation is suspected.
  • Possible war crimes must be promptly investigated.
  • There is no prohibition on commanders investigating possible violations occurring within their own units or committed by others under their control.
  • The fact that subordinate commanders have responsibility to investigate and otherwise repress breaches does not relieve superior commanders of the responsibility to address possible war crimes that have come to their attention and are not being effectively dealt with by those subordinates.
  • Impartiality and independence are questions of fact. The issue is not whether an investigator falls within the chain of command, but whether he or she is in fact able to act without undue influence when making findings as to possible criminal activity.
  • The requisite depth of the investigation and its procedural robustness depend in part on the complexity of the matter and its seriousness.
  • States must take action to punish those who have violated LOAC. Either appropriate disciplinary action (including prosecution) within the military justice system or prosecution by the civilian courts satisfies this requirement.

Concluding Thoughts: The Australian Investigation

Returning to the four-year investigation conducted by the Inspector-General of the Australian Defence Force, it is abundantly clear that Australia has complied with its international law obligations to investigate. Indeed, the scope, depth, and procedural rigor of the investigation went well beyond what is required under international law. In fact, Australia is currently conducting a criminal investigation that will likely result in prosecution of multiple offenders. Australia is to be commended for the professionalism, quality, and comprehensiveness of the investigation.

However, caution is warranted in using the investigation as a model for compliance with obligations regarding war crimes. It reflects the practice of a State that operates on the high-end of investigative processes and procedures, and few States will likely be able to muster the resources necessary to conduct investigations at this level. Nevertheless, as a matter of both treaty and customary LOAC, States must conduct independent, effective, prompt, and impartial investigations into possible war crimes. The failure to do so is unlawful. As importantly, doing so is essential not only to safeguard the rule of law during armed conflict, but also to maintain the discipline that is essential to success on the battlefield.


Lieutenant Colonel Durward Johnson serves as Military Professor of International Law and Associate Director for the Law of Land Warfare at the Stockton Center for International Law at the U.S. Naval War College.

Michael N. Schmitt is the G. Norman Lieber Distinguished Scholar at the United States Military Academy. He is also Professor of Public International Law at the University of Reading, Strauss Center Distinguished Scholar and Visiting Professor of Law at the University of Texas, and Charles H. Stockton Distinguished Scholar-in-Residence at the United States Naval War College.

The views expressed here are their own and do not represent those of the U.S. Naval War College, the Department of the Navy, the Department of Defense, or any part of the U.S. government.