93. [T]he Appeals Chamber considers that even though Šljivančanin no longer had de jure authority over the military police deployed at Ovčara, had he ordered the military police not to withdraw, these troops may well have, in effect, obeyed his order to remain there, considering he had been originally vested with the authority for the entire evacuation of the Vukovar Hospital and entrusted with responsibility for protecting the prisoners of war. In particular, Šljivančanin could have informed the military police deployed at Ovčara that Mrkšić’s order was in breach of the overriding obligation under the laws and customs of war to protect the prisoners of war, and thus constituted an illegal order.

94. Indeed, issuing an order contrary to Mrkšić’s to the military police of the 80 mtbr was a course of action that would have required Šljivančanin to go beyond the scope of his de jure authority, which had been effectively removed by virtue of Mrkšić withdrawal order.[1] Nonetheless, the illegality of Mrkšić’s order required [ljivančanin to do so. To further support this conclusion, the Appeals Chamber recalls the analysis in the Čelebići Trial Judgement which implies that in the context of preventing the commission of a war crime, an officer may be expected to act beyond the strict confines of his de jure authority:

Likewise, the finding in the High Command case that a commander may be held criminally liable for failing to prevent the execution of an illegal order issued by his superiors, which has been passed down to his subordinates independent of him, indicates that legal authority to direct the actions of subordinates is not seen as an absolute requirement for the imposition of command responsibility. Similarly, the finding in the Toyoda case, whereby the tribunal rejected the alleged importance of what it called the "theoretical" division between operational and administrative authority, may be seen as supporting the view that commanders are under an obligation to take action to prevent the commission of war crimes by troops under their control despite a lack of formal authority to do so. An officer with only operational and not administrative authority does not have formal authority to take administrative action to uphold discipline, yet in the view of the tribunal in the Toyoda case; "[t]he responsibility for discipline in the situation facing the battle commander cannot, in the view of practical military men, be placed in any hands other than his own.”[2]

Although the Trial Chamber in Čelebići discussed this in the context of superior responsibility, the Appeals Chamber considers that the principle that an officer may be required, within the limits of his capacity to act, to go beyond his de jure authority to counteract an illegal order is equally applicable to the present case.

See also footnote 331:

It is a principle of international humanitarian law that subordinates are bound not to obey manifestly illegal orders or orders that they knew were illegal. See Hostage Case (United States v. Wilhelm List et al., Trials of War Criminals, Vol. XI, p. 1236): “[T]he general rule is that members of the armed forces are bound to obey only the lawful orders of their commanding officers and they cannot escape criminal liability by obeying a command which violates international law and outrages fundamental concepts of justice”. See also Erdemović 1996 Sentencing Judgement, para. 18 (“Although the accused did not challenge the manifestly illegal order he was allegedly given, the Trial Chamber would point out that according to the case-law referred to, in such an instance, the duty was to disobey rather than to obey.”), fn. 12 (“Trial of Rear-Admiral Nisuke Masuda and four others of the Imperial Japanese Navy, Jaluit Atoll Case, U.S. Military Commission, U.S. Naval Air Base, Kwajalein Island, Kwajalein Atoll, Marshall Islands, 7-13 December 1945, Case No. 6, L.R.T.W.C., Vol. I, pp. 74-76, pp. 79-80. See also Trial of Wilhelm List and Others, U.S. Military Tribunal, Nuremberg, 8 July 1947-19 February 1948, L.R.T.W.C., Case No. 47, Vol. VIII, pp. 50-52 […].); Mrđa Sentencing Judgement, para. 67 (“As to the related issue of superior orders, Article 7(4) of the Statute states that ‛[t]he fact that an accused person acted pursuant to an order of a government or of a superior […] may be considered in mitigation of punishment if the Tribunal determines that justice so requires.’ […] [T]he orders were so manifestly unlawful that Darko Mrđa must have been well aware that they violated the most elementary laws of war and the basic dictates of humanity. The fact that he obeyed such orders, as opposed to acting on his own initiative, does not merit mitigation of punishment.”).

625. […] The test for effective control is not the possession of de jure authority, but rather the material ability to prevent or punish the proven offences. Possession of de jure authority may obviously imply such material ability, but it is neither necessary nor sufficient to prove effective control. […]

294.    Article 6(3) of the Statute on “Individual criminal responsibility”, provides that:

The fact that any of the acts referred to in Articles 2 to 4 of the present Statute was committed by a subordinate does not relieve his or her superior of criminal responsibility if he or she knew or had reason to know that the subordinate was about to commit such acts or had done so and the superior failed to take the necessary and reasonable measures to prevent such acts or to punish the perpetrators thereof.

          With respect to the nature of the superior-subordinate relationship, the Appeals Chamber refers to the relevant principles expressed in the Čelebići Appeal Judgement in relation to the identical provision in Article 7(3) of ICTY Statute, as follows:

(i)         [A] superior is “one who possesses the power or authority in either a de jure or a de facto form to prevent a subordinate’s crime or to punish the perpetrators of the crime after the crime is committed”.[1] Thus, “[t]he power or authority to prevent or to punish does not solely arise from de jure authority conferred through official appointment.”[2]

(ii)         “In determining questions of responsibility it is necessary to look to effective exercise of power or control and not to formal titles. […]. In general the possession of de jure power in itself may not suffice for the finding of command responsibility if it does not manifest in effective control, although a court may presume that possession of such power prima facie results in effective control unless proof to the contrary is produced. [T]he ability to exercise effective control is necessary for the establishment of de facto command or superior responsibility and […] the absence of formal appointment is not fatal to a finding of criminal responsibility, provided certain conditions are met.”[3]

(iii)        “The showing of effective control is required in cases involving both de jure and de facto superiors.”

          This Appeals Chamber accepts these statements and notes that the Trial Chamber, in its Judgement, applied a similar approach when it found that:

[E]ven where a clear hierarchy based upon de jure authority is not present, this does not prevent the finding of command responsibility. Equally, as we shall examine below, the mere existence of de jure power does not always necessitate the imposition of command responsibility. The culpability that this doctrine gives rise to must ultimately be predicated upon the power that the superior exercises over his subordinates in a given situation.[5]

Thus, “as long as a superior has effective control over subordinates, to the extent that he can prevent them from committing crimes or punish them after they committed the crimes, he would be held responsible for the commission of the crimes if he failed to exercise such abilities of control”.[6] Therefore, Kayishema’s argument that without de jure authority, there can be no subordinate and hence, no de facto authority, is misconceived. This question turns on whether the superior had effective control over the persons committing the alleged crimes. The existence of effective control may be related to the question whether the accused had de jure authority. However, it need not be; such control or authority can have a de facto or a de jure character.[7]