1 See Major General G. Fay, Investigation of the Abu Ghraib Detention Facility and 205th Military Intelligence Brigade (2004) (hereinafter Fay Report), available at http://files.findlaw.com/news.findlaw.com/hdocs/docs/dod/fay82504-pt.pdf; J. Borger, ‘Cooks and Drivers Were Working as Interrogators’, Guardian, 7 May 2004.

2 See US House of Representatives Committee on Oversight and Governmental Reform, Additional Information about Blackwater USA, 1 October, 2007.

3 See M. Mazzetti, ‘CIA Sought Blackwater's Help to Kill Jihadists’, New York Times, 19 August 2009; J. Warrick, ‘CIA Assassination Program Had Been Outsourced to Blackwater, Ex-Officials Say’, Los Angeles Times, 20 August 2009; E. MacAskill, ‘CIA Hired Blackwater for Al-Qaida Assassination Programme, Sources Say’, Guardian 20 August 2009. Blackwater has since changed its name to Xe Services LLC; see its website http://xecompany.com.

4 See, e.g., Arts. 12 and 39 of the Third Geneva Convention. In relation to occupation, see the Regulations Respecting the Laws and Customs of War on Land, annexed to Hague Convention II of 1899 and Hague Convention IV of 1907, Art. 43.

5 For an analysis of the rules of attribution as applied to PMSCs, see C. Lehnardt, ‘Private Military Companies and State Responsibility’, in S. Chesterman and C. Lehnardt (eds.), From Mercenaries to Markets: The Rise and Regulation of Private Military Companies (2007), 139; M. Spinedi, ‘Private contractors: responsabilité internationale des entreprises ou attribution à l'Etat de la conduite des personnes privées?’, (2005) 7 FORUM du droit international 273; C. Hoppe, ‘State Responsibility for Violations of International Humanitarian Law Committed by Individuals Providing Coercive Services under a Contract with a State’, Centre for Studies and Research of the Hague Academy of International Law (forthcoming).

6 In international armed conflicts, see Additional Protocol I, Art. 91. In non-international armed conflicts, see Art. 4 of the ILC Articles on Responsibility of States for Internationally Wrongful Acts with Commentaries, (2001) 2 (2) Yearbook of the International Law Commission (hereinafter ILC Articles).

7 Ibid., Art. 5.

8 Ibid., Art. 8.

9 See C. Hoppe, ‘Passing the Buck: State Responsibility for Private Military Companies’, (2008) 19 (5) EJIL 989.

10 Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. USA), Merits, Judgment of 27 June 1986, [1986] ICJ Rep. 392, at para. 218. See also Prosecutor v. Tadić, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, ICTY-94–1-AR72 (2 October 1995), para. 102.

11 Emphasis added.

12 Prosecutor v. Kupreskić, ICTY IT-95–16-T, 14 January 2000, at para. 517. See also J. Pictet (ed.), Commentary, Geneva Convention relative to the Protection of Civilian Persons in Time of War (1958), at 15.

13 See L. Boisson de Chazournes and L. Condorelli, ‘Common Article 1 of the Geneva Conventions revisited: Protecting Collective Interests’, (2000) 837 International Review of the Red Cross 67, at 68.

14 Nicaragua, supra note 9, at paras. 219–220, 250.

15 Ibid., para. 220.

16 See J.-M. Henckaerts and L. Doswald-Beck (eds.), Customary International Humanitarian Law (2005), I, Rule 139.

17 Anglo-Iranian Oil Co. case (UK v. Iran), Jurisdiction, [1952] ICJ Rep. 93, at 105.

18 US – Standards for Reformulated and Conventional Gasoline, WTO Doc. WT/DS2/AB/R, adopted 20 May 1996 (App. Body Rep.), at 23. See also Corfu Channel (UK v. Albania), Merits, [1949] ICJ Rep. 4, at 124; Territorial Dispute case (Libyan Arab Jamahiriya v. Chad), [1994] ICJ Rep. 6, at 24; R. Jennings and A. Watts (eds.), Oppenheim's International Law (1992), 1280–1. This principle is one corollary of the general rule of interpretation in Art. 31 of the Vienna Convention on the Law of Treaties (adopted 23 May 1969, entered into force on 27 Jan 1980), 1155 UNTS 331.

19 See University Centre for International Humanitarian Law, Expert Meeting on Private Military Contractors (2005), 43.

20 Convention on the Prevention and Punishment of the Crime of Genocide (adopted 9 Dec. 1948, entered into force 12 Jan 1951), 78 UNTS 277.

21 Case Concerning the Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Bosnia and Herzegovina v. Serbia and Montenegro), Judgment of 26 Feb. 2007 (hereinafter Genocide case, not yet reported), at para. 162.

22 Pictet, supra note 11, at 16.

23 J. Pictet (ed.), Commentary to the Geneva Convention Relative to the Treatment of Prisoners of War (1960), 18.

24 F. Kalshoven, ‘The Undertaking to Respect and Ensure Respect in All Circumstances: From Tiny Seed to Ripening Fruit’, (1999) 2 Yearbook of International Humanitarian Law 3.

25 For a detailed discussion of these operations see P. Singer, Corporate Warriors: The Rise of the Privatized Military Industry (2003); D. Avant, The Market for Force: The Consequences of Privatizing Security (2005).

26 Vienna Convention on the Law of Treaties, supra note 17, Art. 31(3); see also A. Aust, Modern Treaty Law and Practice (2000).

27 For a comprehensive review of the state practice see Henckaerts and Doswald-Beck, supra note 15, II, 3289 ff.

28 Resolution XXIII, International Conference on Human Rights, Tehran (12 May 1968), adopted with no opposing votes.

29 SC Res. 681, 20 Dec 1990, at para. 5.

30 See, e.g., GA Res. 32/91 A, 13 Dec. 1977; GA Res. 37/123 A, 16 Dec. 1982; GA Res. 38/180 A, 19 Dec. 1983; GA Res. 43/21, 3 Nov. 1988.

31 See Henckaerts and Doswald-Beck, supra note 15, I, 510; see also Resolution XXIII, supra note 27, which emphasizes that the obligation to ensure respect for the Conventions is incumbent even upon states that are not directly involved in an armed conflict.

32 GA Res. 60/147, 16 December 2005, UN Doc. A/RES/60/147 (adopted without a vote), para. 3.

33 Ibid., preamble, at 3.

34 Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion, [2004] ICJ Rep. 136 (hereinafter Wall Advisory Opinion), at para. 163.

35 Ibid., at para. 158.

36 Ibid., at para. 50 (Judge Kooijmans, Separate Opinion), citing Kalshoven, supra note 23.

37 Wall Advisory Opinion, supra note 33, at para. 50 (Judge Kooijmans, Separate Opinion).

38 Henckaerts and Doswald-Beck, supra note 15, I, 509.

39 Ibid.

40 See, e.g., A. Duquesne, ‘La responsabilité solidaire des états aux termes de l'article 1 des Conventions de Genève’, (1966) 15 Annales de droit international médical 83; L. Boisson de Chazournes and L. Condorelli, ‘Quelques remarques à propos de l'obligation des Etats de ‘respecter et faire respecter’ le droit international humanitaire en toutes circonstances’, in C. Swinarski (ed.), Studies and Essays on International Humanitarian Law and Red Cross Principles in Honour of Jean Pictet (1984); H. P. Gasser, ‘Ensuring Respect for the Geneva Conventions and Protocols: The Role of Third States and the United Nations’, in H. Fox and M. Meyer (eds.), Effecting Compliance (1993); U. Palwankar, ‘Measures Available to States for Fulfilling their Obligation to Ensure Respect for International Humanitarian Law’, (1994) 34 (298) International Review of the Red Cross 9; F. Azzam, ‘The Duty of Third States to Implement and Enforce International Humanitarian Law’, (1997) 66 Nordic Journal of International Law 55; Boisson de Chazournes and Condorelli, supra note 12; B. Kessler, ‘Die Durchsetzung der Genfer Abkommen von 1949 in nicht-internationalen bewaffneten Konflikten auf Grundlage ihres gemeinsamen Art. 1’, (2001) 132 Veröffentlichungen des Walther-Schücking-Instituts für Internationales Recht an der Universität Kiel 26; B. Kessler, ‘The Duty to “Ensure Respect” under Common Article 1 of the Geneva Conventions: Its Implications on International and Non-international Armed Conflicts’, (2001) 44 German Yearbook of International Law 498; D. Fleck, ‘International Accountability for Violations of the Ius in Bello: The Impact of the ICRC Study on Customary International Humanitarian Law’, (2006) 11 Journal of Conflict & Security Law 182.

41 Fleck, supra note 39, at 181–2; see also Kessler, ‘Die Durchsetzung’, supra note 39, at 195.

42 Nicaragua, supra note 9,at paras. 220, 255.

43 Ibid., at paras. 220, 255.

44 Wall Advisory Opinion, supra note 33, at para. 158.

45 Genocide case, supra note 20, at paras. 425–450.

46 Ibid., at para. 183.

47 Kessler, ‘Duty to “Ensure Respect”’, supra note 39, at 505; for similar comments see N. Levrat, ‘Les conséquences de l'engagement pris par le HPC de “faire respecter” les conventions humanitaires’, in F. Kalshoven and Y. Sandoz (eds.), Implementation of International Humanitarian Law (1989), 279; Kessler, ‘Die Durchsetzung’, supra note 39, at 118; Gasser, supra note 39, at 28.

48 Genocide case, supra note 20, at para. 430.

49 Henckaerts and Doswald-Beck, supra note 15, I, 509 (emphasis added).

50 Genocide case, supra note 20, at para. 430.

51 ILC Articles, supra note 5, Commentary to Art. 14, at para. 14.

52 See generally E. Borchard, Diplomatic Protection of Citizens Abroad (1928), at §87; P. M. Dupuy, ‘Due Diligence in the International Law of State Responsibility’, in Organisation for Economic Co-operation and Development, Legal Aspects of Transfrontier Pollution (1977); R. Pisillo-Mazzeschi, ‘Due diligence’ e Responsabilita Internazionale Degli Stati (1989); R. Pisillo-Mazzeschi, ‘The Due Diligence Rule and the Nature of the International Responsibility of States’, (1992) 35 German Yearbook of International Law 9; J. Hessbruegge, ‘The Historical Development of the Doctrines of Attribution and Due Diligence in International Law’, (2004) 36 New York University Journal of International Law & Politics 265; R. Barnidge, Non-state Actors and Terrorism: Applying the Law of State Responsibility and the Due Diligence Principle (2007).

53 Alabama Claims (US v. Britain) (1871), decided pursuant to the Treaty between Great Britain and the United States for the Amicable Settlement of All Causes of Difference between the Two Countries, Washington, DC (8 May 1871), 142 Consolidated Treaty Series 145. See also J. Moore, History and Digest of the International Arbitrations to which the US Has Been a Party (1898), ch. 68.

54 See, e.g., Home Missionary Society Claim (US v. UK), (1920) 6 Reports of International Arbitral Awards 42; Youmans case, (1926) 4 Reports of International Arbitral Awards 110; Massey case, (1927) 4 Reports of International Arbitral Awards 155; Short v. Islamic Republic of Iran Iran–USCTR (1987); cases in Moore, supra note 52, at 4027–56.

55 Genocide case, supra note 20, at para. 430.

56 ILC Articles, supra note 5, Commentary to Art. 3, at paras. 7–8.

57 For a discussion of the importance of language in identifying due diligence obligations, see Barnidge, supra note 51, at 114–115.

58 Convention Concerning the Rights and Duties of Neutral Powers in Naval War (adopted 18 October 1907, entered into force 26 January 1910), 205 Consol. TS 395, Arts. 8 and 25.

59 Genocide case, supra note 20, at para. 430.

60 Lake Lanoux (Spain v. France), (1957) 24 ILR 123.

61 Convention Respecting the Rights and Duties of Neutral Powers and Persons in Case of War on Land (adopted 18 October 1907, entered into force 26 January 1910), 205 Consol. TS 299, Arts. 4, 5, and 6.

62 GA Res. 2625 (XXV) (24 October 1970), UN Doc. A/8028, at para. 2.

63 Corfu Channel, supra note 17, at 22; see also Barnidge, supra note 51, at 114–15; I. Brownlie, State Responsibility (1983), 42–4, 181–2.

64 Corfu Channel, supra note 17, at 20–2.

65 See, e.g., European Convention for the Protection of Human Rights and Fundamental Freedoms (3 Sept. 1953), 213 UNTS 222, Art. 1; International Covenant on Civil and Political Rights (23 Mar. 1976), 999 UNTS 171, Art. 1(2); American Convention on Human Rights (18 July 1978), 1144 UNTS 123, Art. 1.

66 See, e.g., Human Rights Committee, General Comment 6, UN Doc. A/37/40 (1982); Human Rights Committee, General Comment 31, UN Doc. CCPR/C/21/Rev.1/Add.13 (2004), at para. 10; Velásquez Rodríguez v. Honduras, (1988) 4 IACtHR Ser. C, at paras. 48, 172; Kaya v. Turkey, ECHR Rep. 2000-III 149, at paras. 101, 108–109.

67 Human Rights Committee, Concluding Observations, Lesotho, UN Doc. CCPR/C/79/Add.106 (1999), at para. 19 (emphasis added).

68 Alonso Eugénio da Silva v. Brasil, IACommHR Case 11.598, Rep. No. 9/00 (24 Feb.1999), para. 33.

69 GA Res. 60/147, supra note 31, at para. 3.

70 Ibid., at para. 3.

71 Ibid., preamble, at 3.

72 Of course, General Assembly resolutions do not constitute a formal source of law within the categories in Art. 38(1) of the Statute of the ICJ, and the General Assembly does not generally have the legal power to make law or to adopt binding decisions under the UN Charter. Nonetheless, as General Assembly resolutions purporting to declare principles of law constitute official expressions by the states concerned, they may be treated as relevant evidence of the propositions of law that they embody, and a state's vote in favour of a law-declaring resolution may constitute an expression of opinio juris regarding the norms articulated therein: see Nicaragua, supra note 9, at paras. 188, 202; Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, [1996] ICJ Rep. 66, at para. 70; I. Sinclair, ‘The Significance of the Friendly Relations Declaration’, in V. Lowe and C. Warbrick (eds.), The UN and the Principles of International Law (1994); O. Schachter, ‘General Course in Public International Law’, (1982-V) 178 RCADI 111, at 116–18.

73 Y. Sandoz, C. Swinarski, and B. Zimmermann (eds.), Commentary on the Additional Protocols of 8 June 1977 to the Geneva Conventions of 12 August 1949 (1987), at para. 3660 (emphasis added). In support of this contention, the ICRC cites a 1951 work by Marcel Sibert, which states that the government ‘doit exercer toute la diligence nécessaire, soit pour empêcher ces faits de se produire, soit pour assurer leur répression s'ils se sont produits’. M. Sibert, Traité de droit international public (1951), I, 317 (emphasis in original).

74 Case Concerning Armed Activities in the Territory of the Congo (DRC v. Uganda), (2005) ICJ Rep. 168, para. 178.

75 Ibid., at para. 179 (emphasis added).

76 Alabama Claims, supra note 52, at 612 (emphasis added).

77 Pisillo-Mazzeschi, ‘Due Diligence Rule’, supra note 51, at 44.

78 Barnidge, supra note 51, at 138.

79 Genocide case, supra note 20, at para. 430.

80 US Diplomatic and Consular Staff in Tehran (US v. Iran), [1980] ICJ Rep. 3, at para. 68 (emphasis added).

81 See ILC Draft Articles on the Prevention of Transboundary Harm from Hazardous Activities with Commentaries (2001) II (2) Yearbook of International Law, Commentary to Art. 3, at paras. 12, 17; Report of the United Nations Conference on Environment and Development, Rio de Janeiro, June 1992, Vol. I: Resolutions adopted by the Conference, Res. 1, Ann. I.

82 Singer, supra note 24, at 121; Avant, supra note 24, at 101–13; K. Silverstein, ‘Privatising War’, The Nation, 28 July–4 August 1997, 4.

83 A. Epiney, Die voelkerrechtliche Verantwortlichkeit von Staaten für rechtswidriges Verhalten im Zusammenhang mit Aktionen Privater (1992), 249.

84 Alabama Claims, supra note 52, at 572–3, 613; see also ILC Draft Articles on Transboundary Harm, supra note 80, Commentary to Art. 3, at para. 11; Sibert, supra note 72, at 317.

85 To use the terminology of the ICJ in Nicaragua, supra note 9 (at para. 218) in relation to the obligations in Common Article 3; see also the Tadić jurisdiction appeal, supra note 9, at para. 102.

86 See ILC Articles, supra note 5, Arts. 2 and 12, Commentary to Art. 2, at paras. 3, 10; Brownlie, supra note 62, at 37–48; R. Higgins, Problems and Process: International Law and How We Use It (1994), 159–61.

87 Keenan v. UK, ECHR 2001-III, para. 89, quoting Osman v. UK, ECHR 1998-VIII, at para. 116; see also Kilic v. Turkey, ECHR 2000-III, at paras. 65–68.

88 Genocide case, supra note 20, para. 431. See also the cases in Moore, supra note 52, at 4027–56, in which the Tribunal held the state responsible for a failure to prevent certain activities on its territory which the state ought to have discovered through diligent investigation.

89 ILC Draft Articles on Transboundary Harm, supra note 80, Commentary to Art. 3, at para. 18.

90 See GA Res. 60/147, supra note 31, paras. 2–3. In the context of human rights law, states have a specific obligation to enact legislative and other measures to protect human rights, in addition to the obligation to prevent, suppress, and punish particular violations: see, e.g., American Convention, Art. 2; ICCPR, Art. 2. In the context of environmental law, see ILC Draft Articles on Transboundary Harm, supra note 80, Commentary to Art. 3, at para. 10. More generally see Pisillo-Mazzeschi, ‘Due Diligence Rule’, supra note 51, at 26–30; Borchard, supra note 51, at §86.

91 In Alabama Claims, for example, Britain could not plead the insufficiency of its neutrality legislation to escape liability for failing to prevent the violation by private individuals of British neutrality; see also Baldwin (US) v. Mexico (11 April 1838) in Moore, supra note 52, at 2623; Noyes (1933) 6 Reports of International Arbitral Awards 308, at 311; Kennedy (1927) 4 Reports of International Arbitral Awards 194, at 198; E. Hall, International Law (1924), at 641–2.

92 Wall Advisory Opinion, supra note 33, at para. 50 (Judge Kooijmans, Separate Opinion).

93 Standard Minimum Rules for the Treatment of Prisoners, Adopted by the First UN Congress on the Prevention of Crime and the Treatment of Offenders (Geneva, 1955) and approved by the Economic and Social Council by its Res. 663 C (XXIV) of 31 July 1957 and 2076 (LXII) of 13 May 1977, Art. 46(1).

94 Doswald-Beck argues that an obligation on states to train anyone they hire is inevitably part of the duty to ‘ensure respect’ in Common Article 1: see Doswald-Beck, ‘Private Military Companies under International Humanitarian Law’, in Chesterman and Lehnardt, supra note 4, at 133.

95 UN Convention against Torture, 10 December 1984, 1465 UNTS 85 (emphasis added).

96 Standard Minimum Rules, supra note 92, Art. 47(2).

97 Basic Principles on the Use of Force and Firearms by Law Enforcement Officials Adopted by the 8th UN Congress on the Prevention of Crime and the Treatment of Offenders, Havana, 1990, at para. 18.

98 Nicaragua, supra note 9, at para. 122.

99 Ibid., at para. 255.

100 See D. Isenberg, ‘Challenges of Security Privatisation in Iraq’, in A. Bryden and M. Caparini (eds.), Private Actors and Security Governance (2007).

101 See Fay Report, supra note 1, at 52.

102 Ibid., at 50–2.

103 See, e.g., US Department of Defense Instruction 3020.41 (3 October 2005); US Department of Defense Directive 2311.01 E (9 May 2006).

104 Isenberg, supra note 99. These problems came to light dramatically in the aftermath of the Blackwater shooting in Baghdad in September 2007, in which 17 civilians were killed. See US Congress Committee Report, supra note 2.

105 This reflects the test utilized by the ICJ in the Genocide case, supra note 20 (at para. 430), as well as by the European Court of Human Rights in assessing the obligation to protect life in Keenan v. UK, supra note 86 (at para. 89), and Osman v. UK, supra note 86 (at para. 116).