While a mere pattern of treaty provisions is not sufficient,21 concordant laws/practice may establish a presumption. In a few cases, courts have held rules to exist under customary international law where the concordant practice leads to presumption of opinio juris.22 With practice established and opinio juris presumed, customary international law is proved. While this position was explicitly rejected by the Extraordinary Chambers in the Courts of Cambodia (ECCC),23 the Special Tribunal for Lebanon (STL) agreed that concordant practice alone is not sufficient for a rule to exist under customary international law, but it could if it was paired with the concern of the international community.24 In any event the ECCC also held that a norm of customary international law could be evidenced by authoritative scholars, 25 so its position might not have been severe as this statement suggests. Provided the issue is one of significant international concern, practice reflecting efforts to resolve the problem can result in a presumption. Similarly, issues on which the international community has expressed concern are generally more likely to be customary international law. This likelihood could result from an articulated concern over a problem26 or negotiations that might result in a treaty document, where the negotiations themselves helped to crystallize the norm.27 In some cases, international concern might alone rise to the level of a Mainz, 1998 ECR I-3655, para. 50; Gabčíkovo-Nagymaros Proj. (Hung. v. Slovk.), Judgment, 1997 ICJ 7, para. 104 (Sept. 25). See Juris. Imms. case, at paras. 67-72. 20 See Juris. Imms. case at para. 57; Gulf of Maine case, supra note 6; Pros. v. Ayyash, Case No. STL-11-01/I, Interloc. Dec. on the Appl. L: Terrorism, etc., (Ayyash case, Interloc. Dec. on the Appl. L) para. 86 (Spec. Trib. for Leb., Feb. 16, 2011); Bow St. Metro. Stipend. Magist., ex p. Pinochet Ugarte (No. 3) (Pinochet (No. 3) case), 2 WLR 827, paras. 56-8 (H. Lords, UK, 1999); Int’l L. Assoc., Comm. on Form. of Customary (Gen.) Int’l L. Assoc., Maurice Mendelson, et al., Statement of Principles Applicable to the Formation of General Customary International Law, Final Report of the Committee (2000) (ILA Statement of Principles). See Ayyash case, Interloc. Dec. on the Appl. L, supra note 20 at para. 101 21 See ILA Statement of Principles, Prin. 22 (“The fact that a treaty permits reservations to all or certain of its provisions does not of itself create a presumption that those provisions are not declaratory of existing customary law … There is no presumption that a succession of similar treaty provisions gives rise to a new customary rule with the same content”). 22 See Ayyash case, Interloc. Dec. on the Appl. L, supra note 20 at para. 101. Also see Wimbledon case; Nottebohm Case at 22; N. Sea Cont. Shelf cases, at 231 (Feb. 20) (Lachs, J, diss. op.); id. at 246-47 (Sørensen, J. diss. op.); CLIVE PARRY, THE SOURCES AND EVIDENCE OF INTERNATIONAL LAW 62 (1965); LAUTERPACHT, DEVELOPMENT OF INTERNATIONAL LAW at 380; WILFRED JENKS, THE PROSPECTS OF INTERNATIONAL ADJUDICATION 253-4 (1964); CHARLES DE VISSCHER, THEORY AND REALITY IN PUBLIC INTERNATIONAL LAW 441 n.19 (1968); Richard Baxter, Treaties and Custom, 129(I) REC. DES COURS HAGUE ACAD. INT’L L. 25, 69 (1970). 23 See Case No. 002/19-09-2007-EEEC/OICJ (PTC38), Dec. on the Appls Ag. the Co-Investig. Judges Order on Joint Crim. Enterprise (JCE), para. 53 (Extraord. Chs. in the Cts of Camb., Pre-Tr. Ch., May 20, 2010) (“A wealth of state practice does not usually carry with it a presumption that opinio juris exists”) 24 See Prosecutor v. Ayyash et al., Case No. STL-11-01/I/AC/R17bis, Interlocutory Decision on Applicable Law: Terrorism, Conspiracy, Homicide, Perpetration, Cumulative Charging, para. 91 (Spec. Trib. for Lebanon Feb. 16, 2011) However, the mere existence of concordant laws does not prove the existence of a customary rule, ‘for it may simply result from an identical view that States freely take and can change at any moment.’ … To turn into an international crime, a domestic offence needs to be regarded by the world community as an attack on universal values (such as peace or human rights) or on values held to be of paramount importance in that community; in addition, it is necessary that States and intergovernmental organisations, through their acts and pronouncements, sanction this attitude by clearly expressing the view that the world community considers the offence at issue as amounting to an international crime.” (citation omitted)). 25 See Case No. 002/19-09-2007-EEEC/OICJ (PTC38), Dec. on the Appls Ag. the Co-Investig. Judges Order on Joint Crim. Enterprise (JCE), para. 53 (Extraord. Chs. in the Cts of Camb., Pre-Tr. Ch., May 20, 2010) (“authoritative pronouncements”) 26 See also Pinochet case (No. 3) paras. 56-58; Ayyash, Case No. STL-11-01/I, ¶ 86 (citing, inter alia, Report to the CounterTerrorism Committee (Iran), UN Doc. S/2001/1332, at I (Dec. 27, 2011) (“As a preliminary matter, there is no doubt that there is a commonly shared agreement on the need to ‘fight international terrorism in all its forms and irrespective of its motivation, perpetrators and victims, on the basis of international law’”). 27 See L.B. Sohn, Unratified Treaties as a Source of Customary International Law, in A. B OS & H. S IBLESZ , EDS ., R EALISM IN L AW -M AKING : E SSAYS IN INTERNATIO NAL L AW IN HONOUR OF W ILLEM R IPHAGEN 245-6 (1986) The Court is thus willing to pay attention not only to a text that has codified a pre-existing customary law but also to one that has crystallized an “emergent rule of international law”. It is sufficient for that purpose to have the rule in question adopted by an international conference by consensus or … without a dissenting voice … A new rule is created by its general acceptance by all States concerned… If most States, including almost all States having a special interest in the application of the rule, act in accordance with it, there is a clear presumption that the rule agreed upon at the conference, though the agreement has not yet been ratified, has become an accepted rule of customary international law 4 Electronic copy available at: https://ssrn.com/abstract=3091912