Legal scholar Kevin Jon Heller examines the legal and evidentiary justifications for U.S. "signature" strikes—drone attacks that target unknown individuals based on a behavioral pattern—and finds that both frequently fail to meet the requirements of international humanitarian law.

International Institute, UCLA, April 9, 2013—The United States clearly believes that using lethal force against suspected terrorists is legal, said legal scholar Kevin Jon Heller, as long as it conforms with Article 51 of the U.N. Charter (the right of states to defend themselves against armed attack). Heller spoke at a lecture organized by the UCLA Burkle Center for International Relations and the Sanela Diana Jenkins Human Rights Project of the UCLA School of Law.

“Signature strikes,” explained Heller, make up the overwhelming majority of drone attacks carried out by the United States. These strikes target individuals whose identities are unknown, but who exhibit certain patterns of behavior or defining characteristics associated with terrorist activity. In contrast, “personality” strikes target specific, known individuals, such as the strike that killed American-born Anwar al-Awlaki in Yemen in October 2011.

“It is critically important to understand that an extra-territorial targeted killing potentially violates two different, but equally fundamental, rights under international law,” said Heller. First, it could violate the right of the affected state to territorial sovereignty, as protected under Article 24 of the U.N. Charter. Second, it could violate the targeted individual’s right to life, as protected under Article 6 of the International Covenant on Civil and Political Rights (ICCPR).

Even if a U.S. signature strike can be considered a necessary proportionate response to an armed attack, Heller insisted that this did not mean that the use of deadly force against an individual was legal—a distinction the United States does not seem to understand.

In other words, he continued, the United States must be able to justify both the violation of a state’s right to sovereignty (e.g., citing self-defense under Article 51 of the U.N. Charter) and the denial of an individual’s right to life (either under the rules of international humanitarian law if the killing takes place in an armed conflict, or under the rules of international human rights law if it takes place outside of armed conflict).

The United States takes the position that all of its signature strikes are governed by international humanitarian law (IHL) and not international human rights law, a point disputed by Heller. Even so, he said, not all such strikes necessarily comply with IHL.

“To determine the legality of any particular strike, we must ask two interrelated questions,” said the speaker. “Was the particular signature legally sufficient to establish that the victim of the signature strike was targetable? Was the evidence sufficient to determine that the targeted individual was engaged in the signature behavior?” A signature strike is legal only when the answer to both questions is “yes,” argued Heller.

Using these requirements of legal and evidentiary adequacy, the speaker examined several of the some 14 (or more) “signatures” used to justify U.S. drone strikes on unknown individuals. In his view, two types are legally justified: strikes against unknown individuals who are transporting weapons and attacks on known Al Queda compounds.

In the first case, however, he specified that individuals cannot be attacked simply for being armed (for example, nearly all men in Yemen are armed). In the second case, he specified that a compound used primarily for civilian purposes is only legally targetable when it is being used for military purposes.

Using the same criteria, Heller found that three types of signature strikes are never legal because they blatantly violate the evidentiary requirement. These are strikes against:

• military-aged males in an area of known terrorist activity (a category that Heller deemed an unfortunate remnant of the Vietnam War);
• individuals who “consort” with known militants; and
• groups of armed men traveling in trucks in areas currently under the control of Al Queda.

Finally, Heller claimed that one signature — “facilitating terrorist activity” — was inherently neither legally adequate or inadequate, as it depended on how the United States interpreted the conditions in question.

In his view, direct participation in hostilities, gathering military intelligence in enemy territory, acting as a guide for an organized armed group, or providing ammunition during hostilities fulfilled the requirements of legal adequacy for this signature. However, “war-sustaining activities” such as recruitment, propaganda, fighters, financing, or providing fighters food, lodging, or logistical support, did not.

With respect to the evidentiary adequacy of signature strikes, Heller identified two main challenges: lack an international standard for the level of certainty required to target unknown individuals and lack of transparency on the part of the U.S. government. The government won’t make public either the signatures or the evidence it uses to justify signature strikes (asserting that the information is “classified”), he observed, which makes it difficult to judge their legality.

Numerous documented cases of incorrect targeting and the killing of innocent civilians, however, indicate insufficient evidence of a “signature” prior to strikes, said Heller. He noted that the inability of drones to distinguish individuals in very densely populated urban areas or in areas covered with vegetation was also responsible for incorrect targeting.

Heller concluded that the United States was clearly willing to launch signature strikes on the basis of evidence that was anything but definitive.  He noted that in order to confirm certain signatures (e.g., behavior indicating that an individual is a member of an armed organized group), individuals need to be tracked over time, based on analysis of communication intercepts and intelligence from human sources.

Yet, signature strikes have overwhelmingly targeted low- and middle-level militants, he continued, who are unlikely to be the object of specific, resource-intensive investigations. Moreover, added Heller, the most controversial signature strikes take place in areas highly unlikely to have signal intercepts or human sources, such as the Federally Administered Tribal Areas (FATA) in Pakistan and areas of Yemen.

The speaker ended his talk with several key observations. “The belief of the United States that the self-defense clause of the U.N. Charter justifies depriving an individual of his right to life is simply inaccurate," he said. "In addition, the United States appears to have launched drone strikes on the basis of a number of signatures that are either per se unlawful or are only lawful if interpreted in a manner not suggested by U.S. practice. And there are significant questions about whether the United States demands evidence of targetability sufficient to rebut the presumption of civilian status under international humanitarian law.”

Kevin Jon Heller is Associate Professor & Reader at the Law School of Melbourne University, Australia. A permanent member of the international law blog “Opinio Juris,” he is also Project Director for International Criminal Law at the Asia Pacific Centre for Military Law, a joint project of Melbourne Law School and the Australian Defence Force. Click here for a copy of the “Journal of International Criminal Justice” article on which his lecture was based.