The problem of concurrent jurisdiction is compounded by the absence of a transnational ne bis in idem principle. Domestic courts generally may not prosecute an individual for a crime for which they have been acquitted or convicted, but “it is widely accepted…that the principle is not applicable at the transnational level.”11 In a situation in which a territorial state or the state of nationality (a “nexus-state”) has already rendered a verdict (and even when the accused has served her sentence), a bystander state (which perhaps arrests the accused) may exercise “not complementary, but primary and original” jurisdiction.12

The absence of an international ne bis in idem principle, and the issue of concurrent jurisdiction disincentivize states that do want to exercise universal jurisdiction, because they might have to contend with an uncooperative territorial state that refuses to provide critical evidence to the bystander state, or because prosecuting the accused criminal might have undesirable geopolitical consequences.

In a paper on horizontal complementarity, Cedric Ryngaert at the Leuven University and Utrecht University examines the impact that the introduction of a “general ICC-style principle of complementarity” into customary international law would have.13 The full extent of such an impact is outside the scope of this comment. But, the idea of a principle of horizontal complementarity inspired by Article 17 vertical complementarity is intriguing. As Ryngaert explains, such a principle could be a solution to the problems that universal jurisdiction poses.14 In Part II of this comment, I will discuss proposed measures that the Office of the Prosecutor (OTP) can take to facilitate the exercise of universal jurisdiction by states party to the Rome Statute. These steps would likely be part of a policy the OTP would adopt that would address the problem of uncooperative nexus states. Of course, these measures cannot solve the legal problem of concurrent jurisdiction or the lack of a ne bis in idem principle. In Part III of this comment, I explore one solution that would address this problem: the codification of horizontal complementarity in the Rome Statute.

II. Non-Systemic Solutions

Carsten Stahn has observed that “[c]omplementarity enhances observance through threat.”15 And, the OTP is often in a position to make credible threats. Ryngaert explains that the ICC has access to what he calls “multilateral bargaining power.”16 Broadly this is the “legitimacy with which the ICC is imbued” on account of the widespread ratification of the Rome Statute, an independent prosecutor, highly qualified staff, etc.17 A threat by the OTP to investigate a situation in a nexus state is often enough to prompt the state to act. In this case, the OTP’s threat of investigation and prosecution could be used to coerce a state to cooperate with another state invoking universal jurisdiction. This would be somewhat similar to the way the “Pinochet effect” works: In the wake of criminal proceedings in Europe in the 1990s, Chilean prosecutors demonstrated an increased willingness to investigate and prosecute crimes committed during Augusto Pinochet’s regime in Chile.18 National threats of prosecution tend not to have as much coercive power as an international threat of prosecution, because (1) an individual state would lack multilateral bargaining power, and (2) the nexus state may not want to cooperate with the threatening state for unrelated reasons.

Indeed, a threat of investigation and prosecution by the OTP would have more bite than prosecutions even by other international organizations because the ICC may uniquely prosecute sitting heads of state.19 Therefore, a state would likely be more willing to cooperate with a bystander state invoking universal jurisdiction (which cannot prosecute a head of state) if the ICC threatened to investigate.

Of course, threats would likely be necessary only in cases where the nexus state is in some way antagonized by the bystander state’s exercise of jurisdiction. Ryngaert notes that this is not often the case: “The home state will normally welcome [or at least “acquiesce” to] the prosecution by the bystander state.”20 Usually, the accused has fled his home state where he has been sidelined by a new regime that has seized power.

Where there is an absence of antagonism between the nexus state and bystander state, the OTP may step in to facilitate cooperation between the two states, in the name of positive complementarity. In its 2006 Report on Strategy, the OTP explained its expansive view of complementarity to include the “creat[ion of] an interdependent, mutually reinforcing international system of justice” that incorporates “national and international networks” and that “participates in a system of international cooperation.”21 In the context of universal jurisdiction, in which both the nexus state and bystander state are willing to cooperate with the ICC, “positive complementarity means that the Court and the state cooperate with a view to bringing international criminals to justice.”22

Ryngaert notes that “[f]or national prosecutors, it will always be an uphill struggle to mobilize resources for prosecutions that do not directly reduce domestic criminality.” The OTP can always step in and provide resources generally helpful for the prosecution of international criminals that the bystander state lacks. Under Article 93 of the Rome Statute, the ICC may, subject to the consent of all states involved, be a forum for the transfer of evidence relevant to the prosecution of the accused criminal under universal jurisdiction.23

III. Codification as a Systemic Solution

Neither the OTP’s case-specific coercive use of the ICC’s multilateral bargaining power, nor its actions in accordance with its mission of positive complementarity translate into an effective, systemic solution to the problems associated with universal jurisdiction. If making it easier for states to exercise universal jurisdiction is a desirable goal, the codification of horizontal complementarity into the Rome Statute might be an effective solution.

The legislatures of some member states already provide for a horizontal complementarity principle in their own domestic laws. The Code of Criminal Procedure in Germany provides that the federal prosecutor can renounce the prosecution of an act that violates international law if that act is prosecuted by a state on whose territory the office was committed, whose national is suspected of having committed it, or whose national was harmed by it.24 Belgium has a similar provision in its criminal code.25 Neither provision, however, forces the prosecutor to adhere to the principle of horizontal complementarity, but only leaves the matter to her discretion. No other state has a similar provision in their criminal code.26

In her paper on universal jurisdiction and the ICC, Laura Burens explains that a form of horizontal complementarity modelled after Article 17 of the Rome Statute could be used “to guarantee a coherent application of a subsidiary universality principle” between member states of the ICC.27 This “subsidiary universality principle” would authorize a bystander state to step in only when it has “serious reason to believe that the territorial state is manifestly unwilling or unable to prosecute the alleged offender.”28

An amendment to the Rome Statute of this nature would require an amendment under Article 122, according to which any state party may propose the amendment, which would then have to be accepted by consensus, failing which the Assembly of States Parties (ASP) or a Review Conference must adopt them by a two-thirds majority.29 But the amendment process would likely not represent a substantial hurdle. Burens argues that by ratifying the Rome Statute, “member states have indirectly also accepted a complementarity regime on the inter-state level,” because they have “subscribed to the vision of justice underlying the complementarity principle.”30 Even if the acceptance of the complementarity regime does not automatically translate into a legal obligation to respect horizontal complementarity, it does highlight that mutual trust and recognition exists between the member states, by virtue of their shared mission to prosecute mass atrocities, at least within their own territories. If they fail to comply with their obligations, other member states should be able to step in.31 The ICC can play a crucial role here to guarantee that the exercise of jurisdiction by bystander member states is fair, coherent and transparent. An amendment to the Statute codifying horizontal complementarity is therefore in the declared interests of bystander and nexus states.

Horizontal complementarity would not make for a particularly controversial amendment for another reason: it describes obligations and expectations of states parties very similar to those described by the principle of vertical complementarity, as laid out in Article 17 of the Rome Statute. ICC-facilitated horizontal complementarity leans into a passive complementarity reading of Article 17. It provides an alternative to the ICC taking a case another member state wishes to prosecute (and when the territorial state cannot or will not prosecute). The ICC can therefore delegate its cases to member states that, by virtue of their membership, subscribe to the same vision as the ICC.

Codification would solve the problems of concurrent jurisdiction and the absence of a ne bis in idem principle, because a mutually subscribed to third-party—the ICC—would mediate the transfer of the case from nexus state to bystander state. This mediation would require that the nexus state respect the ne bis in idem principle in accordance with provisions analogous to those in Article 20 of the Statute. Article 20 provides that:

No person shall be tried by another court for [an Article 5] crime…for which that person has already been convicted or acquitted by the Court.32

The Court may vice versa not try a crime that has already resulted in conviction or acquittal.33 In addition, the Court could facilitate negotiations between the bystander state and nexus state, in order to ensure that the bystander state’s exercise of universal jurisdiction is appropriate and fair. In case of a extreme dispute that the OTP and the Court do not wish to or cannot resolve, settlement could be found via procedures provided for in Article 119, which permits referral of disputes between states parties to the ASP and the International Court of Justice.34

Finally, in the interests of fairness and transparency, the ICC would be able to monitor proceedings in the bystander court and demand information, that it could share with the nexus state, per Article 18.35 If the monitoring OTP determines that the bystander state is not properly trying the case, or is unjustly delaying the trial, the ICC can always appropriate the case from the bystander state, in accordance with Article 17. In the normal exercise of universal jurisdiction, no similar mechanism in international law exists that would guarantee that universal jurisdiction is being exercised properly.

IV. Conclusion

The OTP has some means by which it could assist states that seek to exercise universal jurisdiction. The OTP could harness the ICC’s multilateral bargaining power to issue credible threats of investigation and prosecution to uncooperative nexus states. And when the state does cooperate, the OTP could facilitate information sharing between the states and provide resources helpful for the prosecution to the bystander state.

But, as Burens notes:

[S]tates usually engage in [universal jurisdiction] prosecutions only if they minimize the risk of political and diplomatic tensions and do not infringe in the sovereignty of other states.36

These risks would be practically neutralized, at least as between member states, if the principle of horizontal complementarity were amended into the Rome Statute along the lines of Article 17 vertical complementarity. Not only would this eliminate the problems of concurrent jurisdiction inherent in the exercise of universal jurisdiction, but would contribute to a harmonization of the prosecution of international crimes. Under a horizontal complementarity regime, the ICC would serve as a forum for the efficient and fair distribution of relevant criminal trials among its member states, especially when the nexus state and bystander state wish to cooperate. The exercise of universal jurisdiction is becoming more common, but it requires the systemic intervention of the OTP, and the ICC generally, to transform universal jurisdiction into a powerful mechanism for prosecuting mass atrocities.

Endnotes — (click the footnote reference number, or ↩ symbol, to return to location in text).

1. 1.

   Cedric Ryngaert, Horizontal Complementarity, in The International Criminal Court and Complementarity: From Theory to Practice 855, 857 (Carsten Stahn & Mohamed M. El Zeidy eds., 2011), paywall, doi. ↩

2. 2.

   Jeffrey L. Dunoff, Monica Hakimi, Steven R. Ratner & David Wippman, International Law: Norms, Actors, Process 290 (Feb. 1, 2020), paywall. ↩

3. 3.

   Ryngaert, supra note 1, at 857. ↩

4. 4.

   Id. at 858. ↩

5. 5.

   Rome Statute of the International Criminal Court, Adopted by the United Nations Diplomatic Conference of Plenipotentiaries on the Establishment of an International Criminal Court, Jul. 17, 1998, U.N. Doc. A/CONF.183/9 [hereinafter Rome Statute], Art. 17(1)(a), available online. ↩

6. 6.

   Id. Art. 5

   (limiting the ICC’s jurisdiction to these crimes). ↩

7. 7.

   Ryngaert, supra note 1, at 858. ↩

8. 8.

   Case Concerning the Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v. Belgium), Judgement, 2002 I.C.J. Rep. ¶ 59 (Feb. 14, 2002) (separate opinion by Rosalyn Higgins, Pieter Kooijmans & Thomas Buergenthal), available online. ↩

9. 9.

   Case Concerning the Arrest Warrant of 11 April 2000 (Democratic Republic of the Congo v. Belgium), Judgement, 2002 I.C.J. Rep. ¶ 16 (Feb. 14, 2002), available online. ↩

10. 10.

    Laura Burens, Universal Jurisdiction Meets Complementarity: An Approach Towards a Desirable Future Codification of Horizontal Complementarity Between the Member States of the International Criminal Court, 27 Crim. L. Forum 75, 77 (2016), paywall, doi. ↩

11. 11.

    Ryngaert, supra note 1, at 860–61. ↩

12. 12.

    Id. at 861. ↩

13. 13.

    Id. at 860. ↩

14. 14.

    Id. ↩

15. 15.

    Carsten Stahn, Complementarity: A Tale of Two Notions, 19 Crim. L. Forum 87, 97–98 (2008), available online. ↩

16. 16.

    Ryngaert, supra note 1, at 863. ↩

17. 17.

    Id. at 862–63. ↩

18. 18.

    See Naomi Roht-Arriaza, The Pinochet Effect: Transnational Justice in the Age of Human Rights (2005), paywall. ↩

19. 19.

    See, e.g., Kenyatta Appears at ICC in Hague for Landmark Hearing, BBC News, Oct. 8, 2014, available online

    (discussing the situation in Kenya, in which President Uhuru Kenyatta was subject to an ICC indictment).

    Press Release, Office of the Prosecutor, ICC, ICC Prosecutor Presents Case Against Sudanese President, Hassan Ahmad Al Bashir, for Genocide, Crimes Against Humanity and War Crimes in Darfur (Jul. 14, 2008), available online

    (discussing the situation in Darfur, Sudan, in which the ICC twice issued warrants for the arrest of then-President Omar al-Bashir). ↩

20. 20.

    Ryngaert, supra note 1, at 864. ↩

21. 21.

    Office of the Prosecutor, ICC, Report on Prosecutorial Strategy 5 (Sep. 14, 2006), available online. ↩

22. 22.

    Ryngaert, supra note 1, at 865. ↩

23. 23.

    Rome Statute, supra note 5, at Art. 93(10). ↩

24. 24.

    Strafprozessordnung [StPO] § 153(f)(2)(4) (in force Jan. 1, 2017) (ger.), available online. ↩

25. 25.

    Belgian Code of Criminal Procedure and Civil Procedure, Art. 10(1 bis), Art. 12 bis (entered into force 2003) (Dut.), available online. ↩

26. 26.

    Ryngaert, supra note 1, at 873. ↩

27. 27.

    Burens, supra note 10, at 78–80

    (outlining what a provision codifying horizontal complementarity might look like). ↩

28. 28.

    Id. ↩

29. 29.

    Rome Statute, supra note 5, at Art. 122(2). ↩

30. 30.

    Burens, supra note 10, at 81. ↩

31. 31.

    Amnesty International, Initial Recommendations for a Convention on Crimes Against Humanity 7 (Apr. 28, 2015), available online

    (explaining that the Preamble to the Rome Statute acknowledges that the existence of universal jurisdiction over crimes against humanity “and the duty, not just the power or right, to exercise this jurisdiction for these crimes”). ↩

32. 32.

    Rome Statute, supra note 5, at Art. 20(2). ↩

33. 33.

    Id. Art. 20(3). ↩

34. 34.

    Id. Art. 119(2). ↩

35. 35.

    Id. Article 18(5)

    (providing that on deferral of a matter to the nexus state, “the Prosecutor may request that the State concerned periodically inform the Prosecutor of the progress of its investigations and any subsequent prosecutions. States Parties shall respond to such requests without undue delay.”). ↩

36. 36.

    Burens, supra note 10, at 96. ↩