Former members of the U.S. military are present in armed conflicts across the globe. Working for private military contractors, they are typically tasked with training and advising foreign armies. But a Buzzfeed article published this week profiles a former U.S. Army lieutenant colonel who has reportedly taken on a commanding role within the United Arab Emirates (UAE) military. American citizen Stephen Toumajan, as Commander of the UAE’s Joint Aviation Command, is responsible for “combat readiness and execution” of all UAE aviation missions. And as Just Security readers well know, the UAE is part of the Saudi-led coalition that has been accused of serious international law violations (including war crimes) for indiscriminate and disproportionate airstrikes in Yemen, arbitrary detention, torture, enforced disappearances, the imposition of a blockade, and closure of Sana’a International Airport.

Yemeni human rights organizations, international groups, and the United Nations have published numerous reports documenting human rights and humanitarian law violations by the Saudi-led coalition. Reports document repeated airstrikes that have resulted in significant civilian casualties, and have concluded that many strikes likely violated international humanitarian law and that some may constitute war crimes (see here, here, here, here, here, here, here, and here). The UN High Commissioner for Human Rights has condemned the airstrikes, and stated that “we are possibly looking at the commission of international crimes.” The UN Secretary General has reported on grave violations against children by the coalition. The UN Panel of Experts, mandated by the Security Council, concluded that here have been “widespread violations” of international law in Yemen, and that the coalition’s closure of Sana’a International Airport “to those genuinely seeking immediate medical treatment abroad” violates Common Article 3 of the Geneva Conventions.  The Panel also found that UAE forces have been responsible for torture, denial of timely medical treatment, and enforced disappearances.

It is no secret that the UAE has been relying on foreign mercenaries in its Yemen operations. The UAE has paid Colombian and Sudanese nationals to serve as part of their ground forces. Lured by Emirati funds, Toumajan is not the first highly-paid ex-military official from a Western nation to take on a leadership role. With foreigners playing an increasingly significant part in the Yemeni war, what criminal prosecution mechanisms are available in the face of serious war crimes allegations?

As discussed in a previous piece, the International Criminal Court could garner jurisdiction over nationals of States that have ratified the Rome Statute. But that is obviously not the situation with respect to U.S. nationals. Moreover, a private military contractor who is no longer on active duty with the U.S. military, cannot be prosecuted under the Uniform Code of Military Justice (UCMJ), which is the usual accountability mechanism for members of the U.S. armed forces. There is another possibility, however: the U.S. War Crimes Act (18 U.S.C. § 2441).

Over two decades old and yet to be used, the War Crimes Act enables the U.S. government to prosecute war crimes committed by U.S. nationals.  Any war crimes prosecution must receive the express approval of the Assistant Attorney General, since complicated foreign policy issues can arise depending on the facts of a given situation. In this case, U.S. support for the Saudi-led coalition that the UAE is part of may give the U.S. government pause. This would be unfortunate. It is hardly in the interests of the U.S. for its ex-service members to be violating the laws of war on behalf of another nation. It is even worse for the United States if such individuals claim that their activities are authorized by the U.S. government. Toumajan told Buzzfeed News that his activities were so authorized, even though the State Department told the news organization that it has never authorized any contractor to provide “direct command functions” to a foreign army.

The precise role of the Joint Aviation Command, which Toumajan apparently commands, and its connection, if any, to serious violations of humanitarian law or war crimes in Yemen is not yet clear. When questioned by Buzzfeed News, Toumajan denied involvement in Yemen. But weighed against this, given the scale of the UAE’s operations in Yemen, is the fact that the Joint Aviation Command controls the aviation assets of the UAE Land Forces, Special Operations Command, and Naval Squadron, and Toumajan’s own claim that he commands Emirati soldiers who are heading into combat. At the very least, the available information raises serious concerns that should be investigated. The UAE has been credibly implicated in international humanitarian law violations and war crimes in Yemen. And many of the most serious allegations of violations implicate policies and practices of the UAE forces, not simply aberrant or rogue acts.

Lt. Gen. Michael X. Garrett shakes hands with Maj. Gen. Stephen A. Toumajan, the commanding general of the Joint Aviation Command, during a visit in the United Arab Emirates March 23, 2016 –Photo by Sgt. Youtoy Martin.

The War Crimes Act prohibits grave breaches of Common Article 3 of the Geneva Conventions, including murder, torture, and cruel and inhuman treatment. These are all offences of which the Saudi-led coalition has been accused in Yemen. (Whether Common Article 3 murder might be more narrowly interpreted to include only killings where the person is “in the power of” the perpetrator, or interpreted more broadly to include civilian deaths resulting from airstrikes carried out in Yemen in violation of international humanitarian law is a difficult question. But the text of the War Crimes Act, with its carve out provision on collateral damage, suggests that U.S. courts might interpret the prohibition to cover such airstrikes).

There are no reports suggesting that Toumajan has personally killed or harmed anyone in violation of the law. But commanders can be held liable for the war crimes of their subordinates. Citing back to the 1945 trial of Japanese General Tomoyuki Yamashita, who the U.S. held liable for atrocities committed by those under his command, the U.S. Department of Defense’s Law of War Manual affirms that commanders must take “necessary and reasonable measures” to stop their subordinates committing war crimes—and that failure to take these measures can result in the commander’s own criminal responsibility. If Toumajan’s Emirati soldiers commit war crimes and he fails to fulfill his responsibilities, the U.S. government could seek to prosecute him under the War Crimes Act.

Due to the extraordinary record of independent reports of international humanitarian law violations and war crimes by the coalition, the U.S. government should seriously inquire into Toumajan’s activities in connection with these allegations. This is a clear instance in which the U.S. government cannot claim that allegations of Saudi and UAE war crimes are taking place beyond the jurisdiction and control of the United States. The War Crimes Act puts this situation squarely within the jurisdiction and control of the United States. It is certainly not meddling in another state’s affairs to reign in a former service member who is telling the world his activities are authorized by the United States.

By taking  these steps, the Trump administration would send a strong message to any would-be mercenaries and contractors that the obligations of American service members to uphold the laws of war do not end simply because they have left the U.S. military to serve a foreign one.