62 Report of the International Law Commission on the work of its fifty-third session breach if it does not “predetermine the final decision to be taken”. Whether that is so in any given case will depend on the facts and on the content of the primary obligation. There will be questions of judgement and degree, which it is not possible to determine in advance by the use of any particular formula. The various possibilities are intended to be covered by the use of the term “occurs” in paragraphs 1 and 3 of article 14. (14) Paragraph 3 of article 14 deals with the temporal dimensions of a particular category of breaches of international obligations, namely the breach of obligations to prevent the occurrence of a given event. Obligations of prevention are usually construed as best efforts obligations, requiring States to take all reasonable or necessary measures to prevent a given event from occurring, but without warranting that the event will not occur. The breach of an obligation of prevention may well be a continuing wrongful act, although, as for other continuing wrongful acts, the effect of article 13 is that the breach only continues if the State is bound by the obligation for the period during which the event continues and remains not in conformity with what is required by the obligation. For example, the obligation to prevent transboundary damage by air pollution, dealt with in the Trail Smelter arbitration,253 was breached for as long as the pollution continued to be emitted. Indeed, in such cases the breach may be progressively aggravated by the failure to suppress it. However, not all obligations directed to preventing an act from occurring will be of this kind. If the obligation in question was only concerned to prevent the happening of the event in the first place (as distinct from its continuation), there will be no continuing wrongful act.254 If the obligation in question has ceased, any continuing conduct by definition ceases to be wrongful at that time.255 Both qualifications are intended to be covered by the phrase in paragraph 3, “and remains not in conformity with that obligation”. Article 15. Breach consisting of a composite act 1. The breach of an international obligation by a State through a series of actions or omissions defined in aggregate as wrongful occurs when the action or omission occurs which, taken with the other actions or omissions, is sufficient to constitute the wrongful act. 2. In such a case, the breach extends over the entire period starting with the first of the actions or omissions of the series and lasts for as long as these actions or omissions are repeated and remain not in conformity with the international obligation. 253 Trail Smelter, UNRIAA, vol. III (Sales No. 1949.V.2), p. 1905 (1938, 1941). 254 An example might be an obligation by State A to prevent certain information from being published. The breach of such an obligation will not necessarily be of a continuing character, since it may be that once the information is published, the whole point of the obligation is defeated. 255 See the “Rainbow Warrior” case (footnote 46 above), p. 266. Commentary (1) Within the basic framework established by the distinction between completed and continuing acts in article 14, article 15 deals with a further refinement, viz. the notion of a composite wrongful act. Composite acts give rise to continuing breaches, which extend in time from the first of the actions or omissions in the series of acts making up the wrongful conduct. (2) Composite acts covered by article 15 are limited to breaches of obligations which concern some aggregate of conduct and not individual acts as such. In other words, their focus is “a series of acts or omissions defined in aggregate as wrongful”. Examples include the obligations concerning genocide, apartheid or crimes against humanity, systematic acts of racial discrimination, systematic acts of discrimination prohibited by a trade agreement, etc. Some of the most serious wrongful acts in international law are defined in terms of their composite character. The importance of these obligations in international law justifies special treatment in article 15.256 (3) Even though it has special features, the prohibition of genocide, formulated in identical terms in the Convention on the Prevention and Punishment of the Crime of Genocide and in later instruments,257 may be taken as an illustration of a “composite” obligation. It implies that the responsible entity (including a State) will have adopted a systematic policy or practice. According to article II, subparagraph (a), of the Convention, the prime case of genocide is “[k]illing members of the [national, ethnical, racial or religious] group” with the intent to destroy that group as such, in whole or in part. Both limbs of the definition contain systematic elements. Genocide has also to be carried out with the relevant intention, aimed at physically eliminating the group “as such”. Genocide is not committed until there has been an accumulation of acts of killing, causing harm, etc., committed with the relevant intent, so as to satisfy the definition in article II. Once that threshold is crossed, the time of commission extends over the whole period during which any of the acts was committed, and any individual responsible for any of them with the relevant intent will have committed genocide.258 (4) It is necessary to distinguish composite obligations from simple obligations breached by a “composite” act. Composite acts may be more likely to give rise to 256 See further J. J. A. Salmon, “Le fait étatique complexe: une notion contestable”, Annuaire français de droit international, vol. 28 (1982), p. 709. 257 See, e.g., article 4 of the statute of the International Tribunal for the Former Yugoslavia, originally published as an annex to document S/25704 and Add.1, approved by the Security Council in its resolution 827 (1993) of 25 May 1993, and amended on 13 May 1998 by resolution 1166 (1998) and on 30 November 2000 by resolution 1329 (2000); article 2 of the statute of the International Tribunal for Rwanda, approved by the Security Council in its resolution 955 (1994) of 8 November 1994; and article 6 of the Rome Statute of the International Criminal Court. 258 The intertemporal principle does not apply to the Convention, which according to its article I is declaratory. Thus, the obligation to prosecute relates to genocide whenever committed. See Application of the Convention on the Prevention and Punishment of the Crime of Genocide, Preliminary Objections (footnote 54 above), p. 617, para. 34.