83 those who in some way made it possible for the perpetrator physically to carry out that criminal act. At the same time, depending upon the circumstances, to hold the latter liable only as aiders and abettors might understate the degree of their criminal responsibility. 193. This interpretation, based on the Statute and the inherent characteristics of many crimes perpetrated in wartime, warrants the conclusion that international criminal responsibility embraces actions perpetrated by a collectivity of persons in furtherance of a common criminal design. It may also be noted that – as will be mentioned below – international criminal rules on common purpose are substantially rooted in, and to a large extent reflect, the position taken by many States of the world in their national legal systems. 194. However, the Tribunal’s Statute does not specify (either expressly or by implication) the objective and subjective elements (actus reus and mens rea) of this category of collective criminality. To identify these elements one must turn to customary international law. Customary rules on this matter are discernible on the basis of various elements: chiefly case law and a few instances of international legislation. 195. Many post-World War II cases concerning war crimes proceed upon the principle that when two or more persons act together to further a common criminal purpose, offences perpetrated by any of them may entail the criminal liability of all the members of the group. Close scrutiny of the relevant case law shows that broadly speaking, the notion of common purpose encompasses three distinct categories of collective criminality. 196. The first such category is represented by cases where all co-defendants, acting pursuant to a common design, possess the same criminal intention; for instance, the formulation of a plan among the co-perpetrators to kill, where, in effecting this common design (and even if each co-perpetrator carries out a different role within it), they nevertheless all possess the intent to kill. The objective and subjective prerequisites for imputing criminal responsibility to a participant who did not, or cannot be proven to have, effected the killing are as follows: (i) the accused must voluntarily participate in one aspect of the common design (for instance, by inflicting non-fatal violence upon the victim, or by providing material assistance to or facilitating the activities of his co-perpetrators); and (ii) the accused, even if not personally effecting the killing, must nevertheless intend this result. Case No.: -94-1-A 15 July 1999