At paragraphs 91 to 97, the Appeals Chamber examined the conditions under which armed forces fighting against the central authorities of the same State in which they live and operate may be deemed to act on behalf of another State, in other words, the conditions under which those forces may be assimilated to the organs of a State other than that on whose territory they live and operate. It concluded:

96. […] [I]n cases such as that currently under discussion, what is required for criminal responsibility to arise is some measure of control by a Party to the conflict over the perpetrators.[1]

97. It is nevertheless imperative to specify what degree of authority or control must be wielded by a foreign State over armed forces fighting on its behalf in order to render international an armed conflict which is prima facie internal.  Indeed, the legal consequences of the characterisation of the conflict as either internal or international are extremely important.  Should the conflict eventually be classified as international, it would inter alia follow that a foreign State may in certain circumstances be held responsible for violations of international law perpetrated by the armed groups acting on its behalf.  

At paragraph 98 the Appeals Chamber gave the following explanation for the need to supplement international humanitarian law general international law rules concerning the criteria for considering individuals to be acting as de facto state organs:

98. International humanitarian law does not contain any criteria unique to this body of law for establishing when a group of individuals may be regarded as being under the control of a State, that is, as acting as de facto State officials.[2]  Consequently, it is necessary to examine the notion of control by a State over individuals, laid down in general international law, for the purpose of establishing whether those individuals may be regarded as acting as de facto State officials.  This notion can be found in those general international rules on State responsibility which set out the legal criteria for attributing to a State acts performed by individuals not having the formal status of State officials.

In the course of a review of the relevant rules of general international law in paragraphs 99–144, the Appeals Chamber observed:

120. One should distinguish the situation of individuals acting on behalf of a State without specific instructions, from that of individuals making up an organised and hierarchically structured group, such as a military unit or, in case of war or civil strife, armed bands of irregulars or rebels.  Plainly, an organised group differs from an individual in that the former normally has a structure, a chain of command and a set of rules as well as the outward symbols of authority. Normally a member of the group does not act on his own but conforms to the standards prevailing in the group and is subject to the authority of the head of the group. Consequently, for the attribution to a State of acts of these groups it is sufficient to require that the group as a whole be under the overall control of the State.

The Appeals Chamber concluded:

137. In sum, the Appeals Chamber holds the view that international rules do not always require the same degree of control over armed groups or private individuals for the purpose of determining whether an individual not having the status of a State official under internal legislation can be regarded as a de facto organ of the State.  The extent of the requisite State control varies.  Where the question at issue is whether a single private individual or a group that is not militarily organised has acted as a de facto State organ when performing a specific act, it is necessary to ascertain whether specific instructions concerning the commission of that particular act had been issued by that State to the individual or group in question; alternatively, it must be established whether the unlawful act had been publicly endorsed or approved ex post facto by the State at issue.  By contrast, control by a State over subordinate armed forces or militias or paramilitary units may be of an overall character (and must comprise more than the mere provision of financial assistance or military equipment or training).  This requirement, however, does not go so far as to include the issuing of specific orders by the State, or its direction of each individual operation. Under international law it is by no means necessary that the controlling authorities should plan all the operations of the units dependent on them, choose their targets, or give specific instructions concerning the conduct of military operations and any alleged violations of international humanitarian law.  The control required by international law may be deemed to exist when a State (or, in the context of an armed conflict, the Party to the conflict) has a role in organising, coordinating or planning the military actions of the military group, in addition to financing, training and equipping or providing operational support to that group.  Acts performed by the group or members thereof may be regarded as acts of de facto State organs regardless of any specific instruction by the controlling State concerning the commission of each of those acts.

47. The Trial Chamber’s finding is also consistent with the holding of the Appeals Chamber in Tadić that “[w]here the controlling State in question is an adjacent State with territorial ambitions on the State where the conflict is taking place, and the controlling State is attempting to achieve its territorial enlargement through the armed forces which it controls, it may be easier to establish the threshold”.[1]  The “overall control” test could thus be fulfilled even if the armed forces acting on behalf of the “controlling State” had autonomous choices of means and tactics although participating in a common strategy along with the “controlling State”.