12.     […] [T]he Appeals Chamber […] appreciates that to hold that a principle was part of customary international law, it has to be satisfied that State practice recognized the principle on the basis of supporting opinio juris. However, it also considers that, where a principle can be shown to have been so established, it is not an objection to the application of the principle to a particular situation to say that the situation is new if it reasonably falls within the application of the principle. Also, in determining whether a principle is part of customary international law and, if so, what are its parameters, the Appeals Chamber may follow in the usual way what the Tribunal has held in its previous decisions.

See also paragraph 52.

143. […] It should be emphasised again that the only reason behind the stated purpose of the drafters that the International Tribunal should apply customary international law was to avoid violating the principle of nullum crimen sine lege in the event that a party to the conflict did not adhere to a specific treaty. (Report of the Secretary-General, at para. 34.) It follows that the International Tribunal is authorised to apply, in addition to customary international law, any treaty which: (i) was unquestionably binding on the parties at the time of the alleged offence; and (ii) was not in conflict with or derogating from peremptory norms of international law, as are most customary rules of international humanitarian law. […]

41. The Appeals Chamber notes that the Trial Chamber considered that Article 3 of the Statute covers not only violations which are based in customary international law but also those based on treaties. It found that Additional Protocol I constituted applicable treaty law in the present case,[1] and found that “whether [Additional Protocol I] reflected customary law at the relevant time in this case is beside the point.”[2]

42. The Appeals Chamber holds that the Trial Chamber’s approach is correct.

43. This approach is consistent with the language of Article 1 of the Statute granting the International Tribunal “competence to prosecute persons responsible for serious violations of international humanitarian law committed in the territory of the former Yugoslavia”. It is also consistent with Security Council Resolution 827 (1993) in which the Security Council expressed its determination “to take effective measures to bring to justice the persons who are responsible for [violations of international humanitarian law]”.[3] These instruments do not impose any restriction to customary international law, which is in line with the statements made in the Security Council at the time the Statute was adopted.[4]

44. The Trial Chamber’s approach is also in line with the Report of the Secretary-General in which he stated that:

the application of the principle nullum crimen sine lege requires that the international tribunal should apply rules of international humanitarian law which are beyond any doubt part of customary law so that the problem of adherence of some but not all States to specific conventions does not arise.[5]

The maxim of nullum crimen sine lege is also satisfied where a State is already treaty-bound by a specific convention, and the International Tribunal applies a provision of that convention irrespective of whether it is part of customary international law.[6]

At paras 81-84, the Appeals Chamber clarified its position in that respect. It concluded:

85. […] while binding conventional law that prohibits conduct and provides for individual criminal responsibility could provide the basis for the International Tribunal’s jurisdiction, in practice the International Tribunal always ascertains that the treaty provision in question is also declaratory of custom.

18. […] While the public interest of protecting the integrity of proceedings through the effective prosecution of offences against the administration of justice cannot be underestimated, it cannot be allowed to undermine the Accused’s rights guaranteed by the principle of legality, which requires sufficient precision and clarity in prescribing modes of criminal liability.[1]

[…]

21. […] [I]n the absence of clear evidence that the doctrine of joint criminal enterprise applies to contempt in customary international law or as a general principle of international law, [the Single Judge] was not satisfied that the Mechanism has jurisdiction over this form of liability for crimes committed in violation of Rule 90 of the Rules.[2] […] [T]he Prosecution’s submissions […] fail to demonstrate the existence of a general principle of law common to all major legal systems or otherwise show error in the Single Judge’s finding.[3]

486. The Appeals Chamber recalls that the ICTY was bound to apply rules of international humanitarian law which are beyond any doubt part of customary international law.[1] The Appeals Chamber further recalls that there is an absolute prohibition on the targeting of civilians in customary international law.[2] However, while the Appeals Chamber of the ICTY has held that an indiscriminate attack may qualify as an attack directed against civilians or give rise to the inference that an attack was directed against civilians,[3] the legal test underpinning the principle of distinction as applied in the law of armed conflict has not been articulated by the Appeals Chambers of the ICTY or the ICTR.[4]

487. The Appeals Chamber observes that the principle of distinction is encapsulated in Additional Protocol I, and that key provisions of Additional Protocol I, including Articles 51 and 52, reflect customary international law.[5] The Appeals Chamber further observes that Additional Protocol I has been relied upon to interpret provisions of the ICTY Statute.[6] The Appeals Chamber therefore considers that, in this instance, the principle of distinction should be interpreted and applied in accordance with the relevant provisions of Additional Protocol I.

488. The Appeals Chamber observes that Article 51(4) of Additional Protocol I prohibits indiscriminate attacks, that is to say, attacks which are of a nature to strike military objectives and civilians or civilian objects without distinction.[7] Thus, in accordance with the fundamental principles of distinction and protection of the civilian population, only military objectives may be lawfully attacked.[8] The widely accepted definition of “military objectives” is set forth in Article 52(2) of Additional Protocol I as “those objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage”.[9]

489. The Appeals Chamber considers that, whether a “military advantage” could have been achieved from an attack requires an assessment of whether it was reasonable to believe, in the circumstances of the person(s) contemplating the attack, including the information available to the latter, that the object was being used to make an effective contribution to military action.[10] The relevant question is whether the attacker(s) could have reasonably believed that the target was a legitimate military objective, and a useful standard by which to assess the reasonableness of such belief is that of a “reasonable commander” in the position of the attacker(s).[11]

See also para. 490 to 501.

[…]

506. […] [T]he Appeals Chamber recalls that “the indiscriminate character of an attack can be indicative of the fact that the attack was indeed directed against the civilian population”.[12] Considering that the Appeals Chamber has affirmed the Trial Chamber’s conclusions that the shelling […] was indiscriminate, an additional finding that the attacks were disproportionate is not necessary to sustain the Trial Chamber’s inference that the attacks were “directed against civilians”.