Editor’s Note: This is Part II of a two-part series. The first article is available here

In an earlier post, we showed that there is a great deal of confusion regarding the scope of war crimes. That confusion threatens to undermine the pursuit of justice. Here we propose a potential solution to the challenges surrounding the definition of war crimes we identified. In an effort to eliminate the confusion that results from over-reliance on prior criminalization, we distill the concept of war crimes down to its essence. A better approach, we argue here and in a forthcoming article, is to define war crimes as consisting of two key elements: (1) a breach of international humanitarian law (IHL) that is (2) “serious.” This approach is not only more jurisprudentially grounded, but it also has several benefits in the context of ongoing prosecutions of Syrian war criminals in Europe.

Addressing Retroactivity without “Criminalization”

Before offering a substantive definition of war crimes, we must first address what has motivated modern international courts to look to prior criminalization as a defining feature of “war crimes.”  As we noted in the last post, while Nuremberg was a signal moment in the evolution of international criminal law, establishing that individuals could be held criminally liable for illegally waged war, the failure of the tribunal to fully and adequately justify individual liability had a corrosive effect on the international criminal law that followed. The introduction of prior “criminalization” as a requirement for a war crime prosecution likely was motivated by desire to avoid this criticism in new war crimes prosecutions—an attempt to ensure that that potential defendants would be put on advance notice of their criminal liability.

Yet the prior criminalization condition has not achieved this goal. It has too often been applied haphazardly and unpredictably by courts, which have looked to a wide array of sources to determine prior criminalization. As a result, the criminalization condition has not always provided the consistency that would be necessary to offer advance notice and thus satisfy the legality condition.

While non-retroactivity is essential to war crimes prosecutions, the prior criminalization condition is not necessary to achieve that principle. It can be just as easily addressed by establishing non-retroactivity as an independent check on the prosecution—a check that is specific to the context in which a particular war crimes prosecution takes place. This approach achieves the goal of ensuring that criminal penalties are not illegitimately applied to activity that was not criminal at the time of its commission, while avoiding much of the confusion, circularity, and uncertainty that currently plagues efforts to define war crimes. We argue for stripping prior criminalization from the definition of a war crime and instead establishing it as an independent condition for the legality of the prosecution.

A Substantive Definition of War Crimes

This approach clears the way for establishing the core features of war crimes untethered from prior criminalization. The definition has two key components. The first is a breach of international humanitarian law. Notably, this formulation excludes those not governed by IHL from prosecution for a war crime. A civilian who commits a crime against a fellow civilian in time of war is not governed by IHL unless that civilian becomes a member of an organized armed group and thereby subject to the obligations of an actor in a non-international armed conflict. Such an actor could be subject to criminal prosecution in domestic court but not for the commission of a war crime.

The second core attribute of a “war crime” is that the IHL breach must constitute a serious violation. Severity is consistently identified by tribunals and scholars as a requirement for a war crime. Scholars and treatises also regularly describe war crimes as “serious violations of IHL.” Indeed, in nearly every significant war crimes prosecution to date, severity was central to the court’s determination that the breach of IHL was criminal in nature.

War Crimes Prosecutions in Domestic Courts

This substantive approach to defining a war crime makes clear that international war crimes are not limited to crimes that can be prosecuted under the current statutes of international tribunals, particularly the Rome Statute. Nothing about a “war crime” requires that it be tethered to these existing statutes, which were crafted to suit the particular circumstances that gave rise to the tribunals at issue.  Domestic jurisdictions may in many cases be better placed to afford a measure of accountability, particular in the context of Syria, and this approach allows them to do so for war crimes not reflected in those statutes, as long as they can meet the independent non-retroactivity condition—and any other limitations on criminal prosecution domestic law may establish.

In the Syrian conflict, for example, many of the most violated IHL provisions in the Syrian conflict are precisely those over which the Rome Statute does not provide jurisdiction. Domestic statutes supplying jurisdiction for war crimes are comparably more open. This is largely because the Rome Statute distinguishes between offenses committed in an international armed conflict (IAC), and non-international armed conflict (NIAC) – the conflict in Syria has been categorized as the latter. Some acts that would be considered prosecutable war crimes during an IAC are notconsidered war crimes during a NIAC under the Rome Statute—such as indiscriminate attacks against civilians. Indeed, a survey of the domestic criminal codes of European states suggests that a number of offenses could be prosecuted domestically in multiple European states as war crimes, even though they could not be prosecuted at the ICC. The domestic penal code of countries like Germany and Finland go beyond the Rome Statute, enhancing the states’ prosecutorial power over war crimes.

Another reason derives from the fact that some international statutes omit important offenses entirely. A noteworthy example is the crime of deliberately inflicting terror on a civilian population, which has occurred frequently in the Syrian war through the use of barrel bombs by the Syrian regime in areas highly concentrated with civilian populations. While the crime of terror is not included as a crime under the Rome Statute, the ICTY held in Galić that infliction of terror on a civilian population does constitute a war crime under international law. Overcoming such inter-tribunal distinctions, a “substantive” definition of war crimes makes obvious that this offense is properly prosecutable as a war crime under either universal jurisdiction, or a domestic statute providing war crimes jurisdiction, given that deliberately inflicting terroris a “serious” breach of IHL.

A substantive definition of war crimes also can help to build consensus across jurisdictional boundaries. In 2016, a German national was charged with “humiliating or degrading treatment” in the Higher Regional Court of Frankfurt for atrocities committed in Syria. While the prosecution argued that humiliating or degrading treatment was an international war crime, strong arguments can be made that the acts in question did not in fact constitute a breach of IHL, a required element of a war crime (in this case, because the act in question might not have had a sufficient nexus to the armed conflict).

Allowing the Law to Evolve

Finally,  a substantive definition of war crimes also helps clarify how to identify new war crimes offenses. A number of crimes committed by both the Syrian regime and certain opposition groups have not been prosecuted at international tribunals before, or if so, only rarely. For instance, as Beth Van Schaak has explained, states continue to disagree over whether use of cluster munitions is per se prohibited under IHL. Similarly, while the prohibition against deliberate starvation of a civilian population is well-established, there have been very few prosecutions of this offense.

The substantive approach to war crimes simplifies the inquiry and eliminates lingering uncertainty regarding whether such offenses need to have been historically punishable as a crime in order to constitute a war crime today. The relevant inquiry to ascertain new crimes is simple: is the offenses an IHL violation, and is it serious? If so, it is a war crime. Whether the crime may be prosecuted in a particular jurisdiction depends on a number of other factors – such as whether it has jurisdiction over the offender (under universal jurisdiction, national, passive personality, effective doctrine, or other principles), applicable immunities, and available evidence.

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As the Syrian War has made clear, violations of the laws of war continue to be numerous and grave. As international institutions and states redress these wrongs—in both domestic and international courts—a substantive approach to the definition of war crimes can help bring a measure of justice.

IMAGE: A woman wears a mask and holds a banner reading “Chemical massacre in Syria” on August 28, 2013 outside the Swedish Parliament in Stockholm, during a demonstration against the mass killings in Syria. (Photo by JONATHAN NACKSTRAND/AFP/Getty Images)