Custom as a Source Under Article 21 of the Rome Statute

Abstract The adoption of the Rome Statute is a significant moment for international criminal law. Before its formulation, the criminal law was governed by the sources mentioned in their statute or Article 38 of the Statute of the International Court of Justice [ICJ Statute]. Custom is one of the important sources within the ICJ Statute. The ad hoc tribunals applied custom and even formulated certain customs. The formulation of custom is considered as against the principle of legality. To avoid such criticism, the State Parties inserted Article 21 in the Rome Statute. The provision clarifies the law which the court can apply. The parties chose not to include custom explicitly. However, the wordings of the provision indicate that the custom is still a source for the court. Apart from the wording of Article 21, other provisions of the Statute give ample scope for the application of custom.

these tribunals because the tribunals' statutes have made an explicit reference to "the laws or customs of war". 4 In the case of the International Criminal Tribunal for the former Yugoslavia [ICTY], the United Nations Secretary-General decreed that the Tribunal should apply only those rules which had become beyond any doubt part of customary law. 5 In the case of the International Criminal Tribunal for Rwanda [ICTR], since their subject matter was not limited to those crimes that have become part of customary international law only, they applied custom and treaty, which were binding upon Rwanda when crimes were committed. 6 The tribunals' statute merely provided the subject matter jurisdiction; the tribunals relied on custom and general principles for further clarifications. 7 At the time of the establishment of these tribunals, international criminal law was still developing. So custom and general principles were used in a gap-filling role by these tribunals. 8 In filling gaps, the tribunal identified criminal law principles that have attained the status of custom, and even went to the extent of formulating the content of international criminal law. 9 This invited severe criticism because applying the unwritten rule in criminal law amounts to a violation of the principle of legality. 10 Another reason for criticism was the law-making attitude of tribunals, which goes against international law's basic premise based on states' consent, which is the sine qua non of international law-making. 11 For example, in the Tadić case, the Appeals Chamber held that the tribunals' jurisdiction is not limited to international armed conflicts; rather, it also extends to non-international armed conflicts. This position of the chamber was in conflict with the plain reading of the ICTY Statute. 12 The chamber tried to justify it by arguing that international law has moved away from a state sovereignty centred approach to a human oriented approach. In the same case, the Appeals Chamber held that Article 3 of the ICTY Statute is not limited to Hague Rules only; rather, it includes all international humanitarian law violations other than the four Geneva Conventions' grave breaches. It was held despite the availability of evidence against it in the form of the Secretary-General's report. 13 To avoid this criticism of violation of the principle of legality, and to formulate the content of international law faced by the ad hoc tribunals, the Rome Statute included a specific provision, Article 21, dealing with applicable law. 14 It is the first criminal statute that expressly prescribes the law to be applied by the court. 15 The inclusion of a provision on applicable law is regarded as a "codified moment" in international criminal law. 16 The inclusion of Article 21 is considered interesting because of its existence, content, and hierarchy. 17 It requires the ICC to apply the Rome Statute, applicable treaties, principles, and rules of international law, general principles of law derived by the Court from national laws of the legal systems of the world, and its own decision. To further restrict the Court, Article 21 creates a hierarchy among the sources. It uses the words such as "in the first place", "in the second place", and "failing that", which suggest hierarchy within its application. 18 Such an interpretation requires the Court to give primacy to the Statute. The Court had also agreed to this view in the Al Bashir case when it held that sources mentioned in Article 21(1)(b) and (c) could only be referred to when there are lacunae in the written statute, elements of crime, and rules and such lacunae that cannot be filled by interpreting it in accordance with Article 21(3) of the Rome Statute and Articles 31 and 32 of the Vienna Convention of the Law of Treaties [VCLT]. 19 In the recent Palestine Judgment, Judge Péter Kovács' Partly Dissenting Opinion has criticized the Court's lacunae-filling approach. He believes that Article 21 does not establish any primacy; rather, it establishes priority. He believes that the Court can restrict itself to sources mentioned in Article 21(1)(a) in simple situations. Still, in complex situations, the Court should not restrict itself from also referring to other sources. 20 The interpretation relates to using custom as an aid to interpretation. Under Article 21, custom has two roles: first as a source, and second as an aid to interpretation. 21 The controversy in this paper is restricted to using custom as a source.
Apart from Article 21, there are also other provisions which suggest limited or no application of custom. Article 22(1) provides that "[a] person shall not be criminally responsible under this Statute unless the conduct in question constitutes, at the time it takes place, a crime within the jurisdiction of the Court". The use of the term "crime within the jurisdiction of the Court" restricts the Court from prosecuting those crimes established by custom. 22 Similarly, Article 25(2) provides that a person who commits a crime within the Court's jurisdiction shall be individually responsible and liable for punishment as per this Statute. Even in this provision, the Court is restricted from using the modes of liability mentioned in the Statute and those which go beyond the Statute. 23 These provisions of the Statute suggest a less significant role of custom within the ICC. 24 The existing literature is divided on whether custom is part of applicable law under Article 21 or not. Some authors believe that, since international criminal law is part of public international law, and custom is a well-established source, custom should be a source even for international criminal law. 25 Others believe that, even if there is no explicit reference to custom, the broad formulation of Article 21 would include custom within the ambit of "principles and rules of international law". 26 While discussing Article 20 of the Draft Statute on Applicable Law, Denmark's representative understood the principles and rules of international law as customary international law. 27 While discussing the crimes within the Court's jurisdiction, Saudi Arabia's representative said that there was no such general international law, so the term should be replaced by customary international law. 28 There is hardly any jurisprudence developed by the ICC which has expressly referred to custom as a source. The main reason for the exclusion of custom is the influence exercised by criminal lawyers. These lawyers believe that if custom is expressly included it will violate the principle of legality. 29 So the question arises as to whether the use of the words "principles and rules of international law" includes custom. This paper will engage with the reasoning behind reading custom within "principles and rules of international law", and whether such a reading would be contrary to the structure of Article 21 and the principle of legality.
Despite the opposing views among authors regarding the inclusion of custom within Article 21, custom has an important role in international criminal law jurisprudence. Before the ICC, custom played an important role in cases before the ad hoc tribunals. For example, the Appeals Chamber in the Tadić case established the customary status of criminalizing serious violations in non-international armed conflict as war crimes. The decision came even though there was no support for it either in the Geneva Convention or in the Additional Protocol. This position gained strength by the subsequent decision of the ICTY. The ICTR has also used custom in the cases before it. In the Akayesu case, it confirmed the customary status of the Genocide Convention. 30 Subsequently, the tribunals in several cases have used custom as a source in cases before them. 31 Even though tribunals have faced criticism for formulating customary law as per their need, the jurisprudence developed by it has helped in the development of international criminal law. 32 Under the Rome Statute, the inclusion of Article 21 has raised several questions as to whether custom is a source under the ICC. Supposing it to be a source, how can it then be applied, bearing in mind the hierarchy established by Article 21 and the lacunae-filling role assigned to it by the court in Al Bashir's case? 33 This paper will look into whether custom can be considered a source under Article 21 of the Rome Statute. The paper then highlights certain instances provided by the Statute itself, which gives scope for applying the custom.

I. Custom as part of Article 21 of the Rome Statute
There are two arguments for reading custom under Article 21. The first one is that international criminal law is part of public international law; hence, the ICC can use the sources mentioned under Article 38 of the ICJ Statute. 34 Article 38 lists custom as a source along with treaties as general principles of law. Even though the provision is aimed at application by the ICJ, it has been used in the discussion by other bodies, including ad hoc tribunals. 35 However, the difference between the ad hoc tribunal and the ICC is 28 Ibid. 29  that the Rome Statute contains a specific provision dealing with applicable law. The availability of a provision on applicable law means that the Court will restrict itself to the Statute's mandate. This is evident from the wording "in the first place" used in Article 21, which means that the Court will first apply the statute, and that it will prevail over other sources. 36 The second argument is that the term used under Article 21(1)(b) is "principles and rules of international law", which is a broad terminology that might also include custom. 37 Custom and general principles are sources of international law as per Article 38 of the ICJ Statute. The difference between Articles 38 and 21 is that the former expressly mentions custom and general principles as a separate source, but the latter does not expressly include custom. Article 21, however, makes a difference between general principles of the law specific to international law and general principles of law derived from national laws. Akehurst believed that international law's general principles are broader principles of international law, including custom and general principles of law. 38 Since Article 21(1)(c) expressly recognizes the general principle of law derived from national law, the only possibility that remains is that it implies custom. 39 The Special Rapporteur's first and second report on general principles also recognizes these two categories of general principles of law. 40 He has also clarified that the term "general principles of international law" or "principles of international law" must be analyzed carefully because in some cases it might be used to refer to the general principles of law formed within the international legal system, or in some cases it might be referring to conventional rules, customary international law, or even general principles of law derived from the national legal system. 41 The reason for using the words "principles" and "rules" is that, in criminal law, the crime is generally committed under government participation or by their tacit approval, so it would be difficult for national courts to prosecute them. Such a nature of international crime makes it hard to detect state practice required for customary law. 42 To avoid this difficulty, the State Parties may have used the term "principles and rules of international law". But, on the other hand, there is also a view that the modern approach of finding custom through the deductive process pays more attention to the general statement of rules and abandons the state practice requirement. 43 The distinction between custom and general principles will become "artificial" or even "illusory" if opinio juris is given more importance than state practice. 44 However, the merging of custom and general principles raises specific problems. 45 First, it would be challenging to reconcile it with Article 38 of the ICJ Statute and Article 21 of the Rome Statute. Both these provisions recognize general principles of law as a separate source, so the merger would mean that Article 38(1)(c) and Article 21 (1)(c) are of no use. Second, the merger might hamper the universal acceptance of both these provisions. The view of reading both these sources together has emerged from a common-law viewpoint. Lord Phillimore, the UK member of the Advisory Committee of Jurists for the Establishment of a Permanent Court of International Justice, argued that general principles came within the scope of customary law. 46 According to this view, custom is the product of legal or moral beliefs or judicial lawmaking, and not state practice and opinio juris. 47 Third, the Court's practice, especially the ICJ, is not consistent with the unitary view of reading custom and general principles together. The Court has referred to "principles" or "general principles" in several cases without clarifying their status. 48 This view justifies the practice of the ICJ in adopting the two-element approach in identifying custom. Whenever state practice has fallen short, it has referred to it as a general principle or principle. 49 Another reason for not reading custom as a source under Article 21 is that the word "general" is deleted from the State Parties' final Statute. The 1994 draft included "general", which has been understood to include customary international law. 50 There is a difference between general and particular norms. Since customary international law binds all states it is a general law; a particular treaty or convention binds only those states which have signed that particular treaty. 51 Conventional norms will only become customary law if supported by sufficient opinio juris, because membership of a particular treaty merely shows state practice. 52

II. The object of Article 21 and custom
Custom has not been included expressly in the Rome Statute because states were aware of the criticism levelled against the ad hoc tribunals. The ICC is a rule-based regime where the rules and standards are publicly declared in advance by the competent authority. This reasoning suggests that formulating and using custom within criminal law would violate the principle of legality. 53 The object of introducing Article 21 was strict adherence to the principle of legality and to limit the power of judges to formulate the content of international law and use custom as and when needed. 54 If the ICC applies custom in ways in which the ad hoc tribunals have applied it, it will frustrate the very object for which a provision on applicable law was introduced. 55 The principle of legality is included in Articles 22, 23, and 24 of the Rome Statute. It requires that prosecution and punishment be based upon the explicit provision of law in force when the crime was committed. The act which constitutes a crime must be "within the jurisdiction of the court". The consequence of using the phrase "within the jurisdiction of the court" is to exclude any possibility of prosecution for offences based solely on customary law. 56 The principle also requires that crimes within the Court's jurisdiction are defined with clarity, precision, and specificity. 57 Pre-Trial Chamber I in the Lubanga Dyilo case observed that there would be no violation of the principle of legality: … if the Chamber exercises its power to decide whether Thomas Lubanga Dyilo ought to be committed for trial based on written (lex scripta), pre-existing criminal norms approved by the States Parties to the Rome Statute (lex praevia), defining prohibited conduct and setting out the related sentence (lex certa), which cannot be interpreted by analogy in malam partem (lex stricta). 58 The rule on specificity and certainty requires the definition of crime to be clear and precise. The rule on non-retroactivity prohibits prosecution for offences which were not declared by law to be an offence when the particular act was committed. The rule of the ban on analogy has been included in Article 22(2), which requires the Court to construe the meaning of a crime strictly. In the case of ambiguity, the interpretation must be made in favour of the accused. Such a requirement by the Court focuses on the importance of determinacy in criminal law.
To comply with the principle of legality, ad hoc tribunals, especially the ICTY, were asked to apply those rules which are "beyond any doubt part of customary law". 59 Since the criminal law was still developing at the international level, ad hoc tribunals' statute had a lot of gaps. In filling those gaps, the tribunal went to the extent of formulating the content of international law. 60 The reason for such criticism was the nature of custom and its method of formation. 61 The principle of legality requires that the law must be written and known to the public in advance. Still, in the case of customary law, it is unwritten, and it is generally founded by the court when any situation requires it. It also gives judges a lot of discretion to ascertain the content of a particular customary law. 62 The uncertainty and imprecise legal content of custom goes against foreseeability and determinacy as required by the principle of legality. The flexibility and changing nature of the constitutive elements of custom (state practice and opinio juris) influence legal certainty. 63 The nature of this has not changed with the enactment of the Rome Statute; this criticism would apply to the ICC's customary law application.

III. The possibility of the application of custom under the Rome Statute
As discussed in the previous section, the inclusion of custom within Article 21 appears debatable. However, the formulation of the Statute leaves scope for the application of custom. However, the application of custom is subject to the fulfilment of two conditions as laid down by the Pre-Trial Chamber in the Al Bashir case. It laid down that customary rules and general principles of law: Such a requirement is needed because of the words "in the second place" in Article 21 of the Statute, implying a subsidiary role to sources other than the Statute itself. The direct application of custom by the ICC has been limited by the hierarchy established by Article 21 and the lacunaefilling role provided to it by the Al Bashir case. There are certain instances in the Statute which probably would require the application of customary law. Those instances are given below. framework of international humanitarian law. Even Article 21(b) directs the Court to apply general principles of international law, including the established principles of the international law of armed conflict. Some aspects of war crime have been declared as customary international law. 65 The Rome Statute refers to international armed conflict and non-international armed conflict, but the Statute has not adopted the definition of these terms. In the earliest cases before it, the Court has to deal with this definition; then, it recognized that the Statute does not define these terms. 66 The Trial Chamber then relied on the definition laid down by the ICTY in the Tadić case because it reflects the customary law. 67 The court in the Bemba Gombo Decision relied on the already established definition of civilian and non-civilian populations. 68 Within the definition of war crimes, there are provisions (Article 8(2)(b) and Article 8 (2)(e)) which use the term "other serious violations of the laws and customs applicable in international or non-international armed conflict, within the established framework of international law". This term is an amalgamation of the older notion of "laws and custom of war" and modern international humanitarian law. Laws and custom of war were used to refer to customary law, so that even within the ambit of Article 8 the Court can rely upon those principles of humanitarian law which have attained the status of customary law. 69 Even the ICC in this direct reference in the Statute itself implies that the Court can directly apply custom.

B. Retroacctive application of the Court's jurisdiction (Articles 12 and 13)
There are two situations under the Statute in which the Court exercises its jurisdiction retrospectively. 70 Article 12(3) deals with a situation in which a state, whether a party to the Statute or not, grants the Court jurisdiction over a situation that has taken place when the state has not accepted the application of the Rome Statute. For example, Ukraine submitted its declaration in 2014 and 2015, but had accepted the Court's jurisdiction since 2013. 71 In the case of Palestine, the declaration was submitted in January 2015, accepting the Court's jurisdiction over crimes since 2014. 72 Similarly, Côte d'Ivoire accepted the jurisdiction of the Court in 2003 over the acts committed in 2002. Later on, Côte d'Ivoire went on to ratify the Rome Statute in 2013. 73 The second situation deals with Security Council referral under Article 13(b). In the case of Security Council referrals, the situation referred to relates to a state that is not a party to it and not subject to the Court's jurisdiction when the act in question took place, for example the situation referred by the United Nations Security Council in Darfur and Libya. 74 One of the requirements of the principle of legality is the non-retroactive application of the Court's jurisdiction. 75 It means that the law that has criminalized the conduct must apply to the accused when it was committed. Apart from applicability, the principle of legality also requires that the law must be accessible and foreseeable to the individual. 76 The application of jurisdiction in these two cases can be justified because the conduct in question has already been prohibited through prior existing customary international law. 77 Even though there is the possibility to use custom as a source to justify the exercise of jurisdiction, the Court has not used it.

C. Mental element (Article 30)
Article 30 refers to the mental element needed to commit a particular crime. It relates only to intent and knowledge as mental elements. There is a possibility of the existence of other mental elements like recklessness and dolus eventualis. The provision begins with the term "unless otherwise provided", which suggests that Article 30 is the default rule in all mental elements, and that there may be deviations where otherwise provided. 78 It has been argued that this term refers to existing customary law, implying that there is a possibility of including any mental element established in customary law even though it has not been mentioned in the Statute. 79 If such understanding exists, it will contradict the hierarchy established by Article 21, which requires the Statute to be given primacy over the other sources. Article 30 would no more be the default rule. It also means that the lower standard mentioned in customary law would be applied instead of the standard in Article 30, which would ultimately violate the principle of legality because criminal law requires that interpretation to be accepted which is in favour of the accused. 80 Through its decision in Bemba Gombo, the ICC has maintained the hierarchy by observing that "Article 30 has to be applied unless the Rome Statute or the Elements of Crimes require a different standard of fault". 81 There are certain crimes which require a mental element other than intent and knowledge. Some of the provisions in war crimes (Article 8(2)(a)(i) and (iii)) mention "wilful" and "wilfully", and the definition of genocide uses "deliberately" (Article 6(c)). The uses of these terms have been reproduced from the definition of war crime and genocide, and these definitions have attained the status of customary law. 82 Such a reference gives further scope for the application of custom.

D. Grounds for excluding criminal responsibility (Article 31)
Article 31 provides grounds for excluding criminal responsibility. It lists incapacity, intoxication, self-defence, defence of another person, and defence of property in war crimes, and duress as grounds for excluding responsibility. Article 31(3) provides that, apart from these grounds, the Court may apply any other ground provided that the ground is derived from applicable law as laid down in Article 21, which is argued to also include customary law. 83 However, in this, it is the Statute itself which refers to the application of customary law. In this case, there are no lacunae that need to be filled. Article 31 does not include an exhaustive list of defences because defences on military necessity or reprisal are not mentioned. 84 These grounds have been established to be a ground for defence within criminal law. 85 When this provision came for discussion before the State Parties, the state's representatives were worried about giving a lot of discretion to the Court's judges. 86 Such a formulation of the provision is considered as a trade-off between the need to repress these crimes and the fundamental rights available to the accused before criminal courts. 87 These circumstances suggest that there is still a role for customary international law within the Rome Statute. With the codification of criminal law, the Court has used it very rarely. There is a need for the ICC to develop a consistent practice to find lacunae and then fill them with the help of custom. Apart from lacunae, as per Article 21, the Court will also have to look at whether it would be "appropriate" to apply a particular customary law. The appropriateness has to be determined by looking at the norm which is to be used and the context in which it is to be applied. 88 In the case against Thomas Lubanga Dyilo, the Trial Chamber held that the procedure of witness preparation before trial is not easily transferable into the system of law created by the ICC Statute and Rule. The Court reached this conclusion by assessing whether this procedure would fit into the system designed by the Statute or not. If it does not fit within it, it would not be appropriate to apply any principles and rules. 89

IV. Conclusion
Custom played a significant role in the development of international criminal law. Before the ICC, the ad hoc tribunals used and formulated custom because there were a lot of gaps in the statutes. The tribunals were criticized for formulating the custom and content of international law as per their need. Such practice goes against the principle of legality. The drafters were aware of the criticisms, so they included Article 21, a specific provision on applicable law. In place of custom, they have used the term "principles and rules of international law", which may imply those principles specific to international law or even customary law. The practice of the Court has not expressly referred to custom as a source. It has referred to and used those principles, which have become part of custom. 90 The main reason for not expressly mentioning it could be the requirements of the principle of legality. The nature and method of formulation of custom stand in contrast to the principle of legality. However, despite the careful drafting, the Statute provides enough scope to use custom as a source in any situation before it.
With regard to the lacunae-filling approach assigned to custom and other sources, the question arises as to whether applying these sources to fill those lacunae will violate the principle of legality or not. The Court needs to clarify what "lacunae" means because cases like the definition of war crimes which directly refer to the international law of armed conflict can be considered as lacunae or not. Whether the use of custom in the circumstances, for example, Article 31, in which the provision allows for the use of custom, will violate the hierarchy and principle of legality. Another question that arises is that the lacunae filled by using custom as a source will be in accordance with the hierarchy established under this provision. The Court's judgments may clarify the confusion as to whether custom is a source under Article 21 or not and the situations in which it can be applied. 90 Dyilo, supra note 67 at para. 533; Gombo, supra note 68 at para. 78 (see ftn 101).