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When does a government’s provision of assistance to foreign armed groups cross the line from legitimate foreign policy to criminal aiding and abetting of those who use the aid to commit atrocities? The question presents one of the most difficult dilemmas in criminal justice, one that has deep normative implications and has provoked sharp splits among the U.S. federal courts and international tribunals that have faced it.

In 2013, the Appeals Chamber of the International Criminal Tribunal for the former Yugoslavia (ICTY) sent shockwaves through international legal circles when it acquitted former Yugoslav Army chief Momčilo Perišić of aiding and abetting atrocities in Bosnia and Herzegovina during the early 1990s. Influenced perhaps by contemporary examples such as U.S. support for Syrian rebels, the Tribunal ruled that “neutral” support to armed groups engaged in combat activities could not give rise to criminal responsibility absent evidence that the support was “specifically directed” toward the group’s unlawful activities. The aftermath of the ruling has produced widespread criticism, but little clarity on how the law should draw the line between legitimate foreign assistance on the one hand and criminal complicity on the other. Domestic legal systems take different approaches to complicity, and even at the international level the law depends very much on which tribunal—and even which particular judge—happens to be deciding a case.

In this Article, I contribute to the debate over the foreign assistance cases by questioning two of its key premises. First, I challenge the pervasive assumption that the resolution of these cases can and should be determined by recourse to the kind of precedential analysis that has dominated judicial consideration of international aiding and abetting cases. As a descriptive matter, the case law is mistaken to maintain that the historical precedents reveal a consistent approach to aiding and abetting that evidences settled principles of customary international law. As a prescriptive matter, international tribunals’ reliance on precedent—however well-founded—is no substitute for the kind of normative analysis that is necessary to secure adequate protections against injustice.

Second, I contest the assumption that the resolution of individual foreign assistance cases turns on the particular doctrinal choices that have divided judges and commentators. Analysis of the competing approaches to aiding and abetting reveals that there is less at stake in the choice of elements than is commonly supposed, because each approach leaves room for substantial flexibility in interpretation and application. Moreover, the most plausible understandings are also the least determinate, suggesting that the resolution of the foreign assistance cases must inevitably rely on complex moral judgments that resist easy encapsulation in the legal elements that have traditionally served to police the boundaries of criminal responsibility.

The combined effect of these insights reveals an indeterminacy that is both inevitable and familiar to criminal law. I conclude by considering how courts might manage this indeterminacy in a way that renders the assignment of criminal responsibility sufficiently predictable while also maintaining a normatively meaningful distinction between guilt and innocence.