Killings in the Caribbean: War Crime or Arbitrary Act?

Since September of last year, the United States has undertaken a series of military strikes on boats in the Caribbean, which are reported to have killed at least 126 people. The first attack on Sept. 2 received particular scrutiny because months later it was reported that a second strike on that day killed shipwrecked survivors. These reports caused an uproar in Congress. After watching a video of the operation, lawmakers called for its release so the public could judge the strike itself. 

Assuming the veracity of the reporting on the Sept. 2 strike, some aspects of the legal analysis are relatively straightforward and can be summarized as follows:

• If the law of armed conflict (LOAC) is not applicable to these strikes, this was an arbitrary killing in violation of the right to life under international human rights law (IHRL). Assuming extraterritorial jurisdiction, no understanding of necessity and proportionality under IHRL could render the killing of the shipwrecked individuals lawful.
• If LOAC is applicable to these strikes, the attack would almost certainly be a violation of LOAC and a war crime. Incidentally, this violation of LOAC would also render the killing a violation of IHRL (General Comment 36, para 64).

Here, I do not wish to consider the legal analysis underpinning either of these claims, or indeed the question of whether the law of armed conflict is applicable to the United States’ wider campaign of strikes in the Caribbean (There has been extensive Just Security coverage of these questions.). Rather, I will consider what follows as a matter of law from determining whether this strike is an arbitrary killing or whether LOAC applies, and it is, in fact, a war crime. Indeed, even if it is the case that the overall result is the same on either account – unlawfulness – and even if it is the case that some legal consequences are, in substance, the same on either account, it is still important to understand  certain diverging implications as a matter of international law flowing from how we characterize the strikes.

Implications That Are in Substance the Same

Assuming the veracity of the reporting on the Sept. 2 boat strikes, the second strike that killed the shipwrecked survivors was unlawful. Here, I highlight two points on which it makes little difference, in substance, as to how the applicable legal framework is characterized: whether it was an arbitrary killing outside of an armed conflict or a war crime.

First, on either account the United States is under a duty to investigate and, where appropriate, prosecute those responsible for the violation. If the law of armed conflict is not applicable, this will be the ordinary application of the positive duty arising under international human rights law to investigate and prosecute individuals responsible for potential unlawful deprivation of life (see para 26 GC36). If the law of armed conflict is applicable, this will be supplemented by the duty of States to investigate, and if appropriate, prosecute war crimes allegedly committed by their nationals or armed forces. 

Second, as to third States and considering potential future strikes of a similar kind, their duties of non-assistance apply no matter which framework is applicable. As Michael Schmitt, Marko Milanovic and Ryan Goodman note, if IHRL is the applicable framework, the obligation in Article 16 ASR not to aid or assist other States in the commission of internationally wrongful acts applies. (Of course, certain doctrinal questions will arise, but none seems particularly troubling in the present instance.) If the law of armed conflict is the applicable framework, the same rule also renders assistance wrongful, complemented by the rule in Common Article 1 of the Geneva Conventions to respect and ensure respect for the Convention “in all circumstances” (for discussion, see here and here). 

Diverging Implications: Jurisdiction, Immunities, and Superior Responsibility

Even if certain implications are, in substance, the same, the characterization of the applicable law in question does have some strikingly divergent implications in relation to individual responsibility. 

First, there is the question of the jurisdiction of third States to prosecute those responsible. On one hand, if LOAC is not applicable, the relevant crime is most likely simply murder in domestic law. Leaving aside the possibility of flag State jurisdiction and/or passive personality jurisdiction in relation to the victims, it will be the United States with jurisdiction under international law to prosecute. International law is not generally understood to allow the exercise of universal jurisdiction in relation to the ordinary domestic law crime of murder. Note, however, that if the strikes rise to the level of crimes against humanity, a number of States may indeed have universal jurisdiction statutes that would allow for prosecution (see below for further discussion on this point). 

By contrast, if LOAC is applicable, on many accounts universal jurisdiction is available for war crimes, which entitles third States with no nexus to the conduct—neither nationality of the perpetrator or victim, nor territoriality—to criminalize and prosecute the offenses. In practice, whether, and under what conditions, States exercise this power is a different question. Suffice it to say, however, that across a number of States, investigations and prosecutions are underway on the basis of universal jurisdiction for crimes committed in non-international armed conflicts.

Second, and relatedly, there is the question of immunities of State officials from foreign criminal jurisdiction. I focus here on immunity ratione materiae, given that, in democracies at least, immunity ratione personae, to the extent it protects particular officials, tends to come to an end. Again, here the question of what law is applicable might matter. As has been widely discussed, at the International Law Commission (ILC), debate has coalesced around Draft Article 7, provisionally adopted by the Drafting Committee on May 12, 2025. In the relevant part, Draft Article 7 provides:

Immunity ratione materiae from the exercise of foreign criminal jurisdiction shall not apply in respect of the following crimes under international law, as defined according to the applicable rules of international law:

…

(c) war crimes

Of course, certain States, including the United States, have objected to the rule formulated in Draft Article 7. Nonetheless, there is quite substantial practice in support of the principle. To give two recent European examples, in 2024 in Germany the Federal Court of Justice, and subsequently the Bundestag, determined that functional immunity does not apply to international crimes (see here and here for analysis). In France, the Court of Cassation determined on July 25, 2025 that functional immunity cannot be invoked in relation to the prosecution of genocide, crimes against humanity, or war crimes. 

For present purposes, the key issue is this: the potential exception to functional immunity is explicitly connected to whether the alleged conduct is an international crime. By contrast, there is little practice relating to the ordinary domestic crime of murder committed by non-nationals of the forum State against non-nationals outside of its territory. On this basis, it may thus really matter whether the conduct constitutes war crimes (or, as discussed further below, one or more crimes against humanity). 

Third, there is the question of who exactly is responsible and the distinctive implications of superior responsibility as it arises under LOAC (and international criminal law). As noted previously, if LOAC is not applicable, the United States is still under an obligation under IHRL to investigate, and where appropriate, prosecute arbitrary deprivations of life. As to who specifically that should be, as I discussed elsewhere (with Dapo Akande), that will ordinarily be those who are responsible for the arbitrary killings. This might be a fact-specific inquiry, taking into account the duty to refuse unlawful orders, as discussed here, as well as the specific contributions and fault of particular individuals. A similar set of considerations would likely arise if LOAC is applicable. Either way, there is little doubt that those who order the alleged wrongful conduct would be responsible and subject to investigation and prosecution. 

If LOAC is applicable, however, there is an additional consideration. Specifically, under  LOAC, the doctrine of superior responsibility expands the ambit of potential individual criminal responsibility (for discussion, see here and here). As a basic framework, as set out by the International Criminal Tribunal for the former Yugoslavia (see e.g. Orić Appeals Judgment para 18), superior responsibility under custom entails the following elements:

• The existence of a superior–subordinate relationship;
• The superior knew or had reason to know that the criminal act was about to be or had been committed; and
• The superior failed to take the necessary and reasonable measures to prevent the criminal act or punish the perpetrator thereof.

Of particular interest is the punishment limb of superior responsibility, particularly as it applies to civilian superiors (for wider discussion of U.S. practice, see Brian Finucane). If LOAC is applicable, this duty to punish does add something as a matter of individual liability. Superiors in the chain-of-command who now fail to discharge their retrospective duties to investigate and punish will themselves be criminally responsible. In relation to the Sept. 2 strike, all superiors—military and civilian, including the commander-in-chief—will without doubt at present meet a standard of “had reason to know.” They will certainly now be in possession of “sufficiently alarming information putting [them] on notice” (Strugar, Appeals Chamber para 304) of potential violations of IHL. Failure to undertake all necessary and reasonable measures to punish the perpetrator(s) will itself ground criminal responsibility under international law.

The Series of Strikes in the Caribbean as a Crime against Humanity

One final point arises. As set out above, international law treats specific instances of arbitrary killing under IHRL—likely prosecuted as (ordinary) domestic law murder—and war crimes under LOAC differently. However, arbitrary killings at a particular scale might themselves be criminalized as the crime against humanity of murder. The critical question will be whether the acts (of murder/arbitrary deprivation of life) were “committed as part of a widespread or systematic attack directed against any civilian population, with knowledge of the attack” (see Art 7 Rome Statute; Art 2 Draft Articles on CAH). 

In the present context, if it is the case that LOAC is not applicable, as Schmitt, Goodman and Milanovic and others argue, then the whole series of strikes must be evaluated as a potential crime against humanity. This is a question that requires further work, particularly in relation to the thresholds of “widespread” or “systematic” and the characterisation of the victims as a civilian population. I note, in this respect, that the New York Times reports that more than 126 people have been killed since September.

For present purposes, an important point follows. If the series of strikes were to be characterized as a crime against humanity, the differences set out above would diminish or disappear. That is to say, if the series of strikes does constitute a crime against humanity, then the distinctive implications of international criminalization set out above—the existence of universal jurisdiction, the absence of immunity ratione materiae, and the doctrine of superior responsibility—would also arise.

Conclusion

As has been widely discussed, States’ attitudes to the applicability and substantive coverage of LOAC, particularly in non-international armed conflicts, have varied over time. Historically, that attitude has been one of caution, evident in the lack of substantive applicability in the Geneva Conventions, other than Common Article 3, to non-international armed conflicts (NIACs), and in the relatively sparse application of conduct of hostilities rules by treaty law to NIACs. More recently, against the backdrop of increased applicability (and enforcement) of IHRL and its more restrictive rules, LOAC’s more permissive regulation of targeting has made it more attractive to certain States as the applicable legal framework. This explains, in part, why the United States is asserting the applicability of LOAC even in the face of real doubts as to that position as a matter of law. 

Even if LOAC brings with it more permissive rules, however, there are distinctive additional legal consequences that follow from possible breaches of those rules. As a matter of international law, on many accounts all States may exercise criminal jurisdiction over war crimes, immunity ratione materiae may be lifted, and the ambit of criminal responsibility would extend to those who failed to exercise their retrospective duties to investigate and prosecute the alleged wrongdoers. These are consequences of the gravity and significance of the categorization of specific conduct as a war crime under international law. 

FEATURED IMAGE: The US Navy warship USS Sampson (DDG 102) docks at the Amador International Cruise Terminal in Panama City on September 02, 2025. Venezuelan President Nicolas Maduro said on September 1, 2025, that eight US military vessels with 1,200 missiles were targeting his country, which he declared to be in a state of “maximum readiness to defend” itself. (Photo by MARTIN BERNETTI/AFP via Getty Images)