Editor’s Note: This piece is part two of a Symposium on the potential benefits and challenges of a single residual mechanism. You can find the introduction and links to all the posts here.

The first post of this Symposium introduced the idea of creating a single residual mechanism that would take over the residual activities of international criminal tribunals after their main prosecutorial activities wind down. This entity would address the core residual functions of current and future ad hoc and hybrid tribunals, namely: archival management, sentence supervision, victim and witness protection, adjudicating contempt of court, and promotion of the tribunal’s legacy. Establishing a consolidated successor organization in the international criminal field, however, raises a number of thorny legal and practical questions: Will tribunals’ charters need to be amended? Whose consent will be required? How will the consolidated residual entity be funded? Will it have a prosecutorial mandate?

This post explores the legal, political, and administrative issues that would need to be addressed prior to the establishment of a single residual mechanism. The discussion in this post, as in Post I and Post III, is informed by a series of interviews conducted with experts in the field of international criminal law with experience in various ad hoc and hybrid international tribunals.

Legal Considerations

Creating a single residual mechanism requires identifying and resolving a number of challenging legal questions: how the mechanism is formed, whether the mechanism possesses a prosecutorial mandate, what triggers would initiate a transfer of duties to the mechanism, and what substantive and procedural law the mechanism would apply. 

1 – Formation and Succession

The first and most fundamental question to answer is which legal instrument should be used to establish the single residual mechanism and facilitate the transfer of residual duties of the underlying tribunals to the mechanism. International institutional law permits creative solutions, so long as certain fundamental international legal principles are followed: 

  • Alteration in Alignment with Founding Instrument: International organizations’ charters must generally be modified in accordance with their constituting legal instruments. In fact, according to Article 39 of the Vienna Convention on the Law of Treaties, a treaty can be amended by agreement between the parties, except “as the treaty may otherwise provide.” International organizations are treaty-based, and their charters may thus be amended or modified only in accordance with the procedures laid out in such charters. The legal instrument facilitating the transfer of tribunals’ residual duties (e.g., the single residual mechanism’s charter, or a U.N. resolution) must take the amendment mechanisms of the respective tribunals’ founding instruments into account. These instruments vary across tribunals and their residual mechanisms. The United Nations Security Council used its Chapter VII powers – which may be binding on U.N. member States – to create the charters of the International Criminal Tribunal for the former Yugoslavia (ICTY), the International Criminal Tribunal for Rwanda (ICTR), and the Special Tribunal for Lebanon (STL), as well as the International Residual Mechanism for Criminal Tribunals (IRMCT) that consolidated the ICTY and ICTR. These charters can only be superseded via a new Security Council resolution under Chapter VII of the U.N. Charter. The transfer of these entities’ functions to a single residual mechanism would therefore have to be approved, or at least not opposed, by the Security Council (including all five of its permanent members).
  • State Consent: Transferring the residual functions of hybrid tribunals would also require the consent of the State party to the tribunal’s founding instrument. The Extraordinary Criminal Chambers in Cambodia (ECCC), Special Court for Sierra Leone (SCSL), and Residual Special Court for Sierra Leone (RSCSL) were formed through bilateral agreements between the U.N. and the relevant State. Additionally, although the STL was established by the Security Council, the relevant Security Council resolution adopted an agreement between the government of Lebanon and the U.N. Secretary General. Therefore, Lebanon, Cambodia, and Sierra Leone would have to consent to the transfer of their respective tribunals’ residual duties to a newly created single mechanism.

2 – Prosecutorial Mandate

Another critical issue concerns whether – and, if so, to what extent – a single residual mechanism would retain the underlying tribunals’ prosecutorial mandate. Prosecutorial powers exist along a sliding scale. At a minimum, the single residual mechanism could retain only the post-conviction capabilities required for the functioning of a residual mechanism, such as the review of petitions for sentence repeals, handling of contempt proceedings, and victim and witness protection issues. On the other end of the spectrum, the single residual mechanism could be designed to take on the full independent prosecutorial capabilities of the transferring tribunals – to hold trials for apprehended indictees, review decisions by the tribunal, and hear appeals by convicted defendants.

There are trade-offs to consider along this spectrum of options. If the single residual mechanism only retains residual prosecutorial duties, outstanding indictments and appeals can be transferred to national courts, subject to monitoring and potential reassignment to national courts based on due-process concerns, such as indefinite pre-trial detention, inhumane conditions of such detention, lack of fair representation and other trial-related issues, irregular sentencing procedures, etc. However, ad hoc and hybrid tribunals are often created to correct the unwillingness or inability of the national jurisdiction to prosecute the perpetrators, to ensure fair trials, or to avoid accusations that prosecutions are merely “victor’s justice” (see here and here for discussions on this issue). All of these issues may resurface if indictees are apprehended after the tribunal concludes its mandate and are accordingly transferred back to the national jurisdiction. The historical record on the success of such transfers is mixed; while transfers from the ICTY to domestic mechanisms in the Balkans were somewhat successful, resulting in the prosecution of more than 600 cases by local authorities in Bosnia and Herzegovina, transfers from the ICTR to the Rwandan judicial system were more fraught, in light of serious concerns that have been raised about Rwanda’s ability to conduct fair trials consistent with international human rights standards.

Any single residual mechanism that retains a prosecutorial mandate would need to consider a number of other factors related to prosecutions, including jurisdictional competence and organizational structure:

  • Jurisdictional Competence: Jurisdictional competence – the authority of a body to conduct legal proceedings related to a given dispute or conflict – is a prerequisite to exercising prosecutorial powers. Depending on how the single residual mechanism is established (i.e. as a standalone entity created by a Security Council resolution, or as a successor to the tribunals created through other means), the single residual mechanism could face serious jurisdictional challenges, including whether its prosecutorial mandate is widely accepted within the international community. Additionally, if the single residual mechanism inherits the prosecutorial capacity of a tribunal, it must ensure the full scale of due process rights the indictees enjoyed under that tribunal’s charter, such as the presumption of innocence, the right to a fair trial, the right to counsel, the right to present evidence and confront witnesses, etc.. The result of adopting the prosecutorial mandates of different tribunals is a complicated patchwork of obligations and expectations within one single residual entity.
  • Organizational Structure: The single residual mechanism’s organizational structure would have to support its prosecutorial mandate. If the single residual mechanism has prosecutorial duties beyond those that are truly residual, its structure would need to include a Registry, a roster of judges, and Offices of the Prosecutor and of the Defense. Moreover, the single residual mechanism’s structure would have to accommodate the particularities of its predecessor tribunals, such as seats reserved for judges representing the relevant national jurisdiction, which were a feature of the SCSL, the ECCC, and the STL. Finally, the single residual mechanism’s budget and administrative planning would need to be flexible to absorb new and unpredictable expenses borne by new trials and appeals.

Giving the single residual mechanism prosecutorial powers is a complex task, although it may be important for the promotion of justice and the legacy of ad hoc and hybrid tribunals. If the single residual mechanism is not granted prosecutorial powers, the successful transfer of the prosecutorial mandates to national jurisdictions would depend on the international community’s willingness to develop and implement safeguards and monitoring to ensure procedurally fair national prosecutions. If such an approach is adopted, a single residual mechanism could help provide support, training, and supervision to national courts handling transferred prosecutions, without becoming involved in the prosecutions directly. Examples of such support provided to national jurisdictions include the various judicial capacity-building measures undertaken by the ICTY and the international community vis-a-vis the Bosnian War Crimes Chamber; the international community’s support toward the Special Criminal Court established in the Central African Republic, as well various other capacity building projects implemented through the U.N. or other international and regional institutions throughout the world.

3 – Trigger Mechanism

A single residual mechanism would need to determine a “trigger” mechanism outlining the conditions that would initiate the transfer of residual duties from the tribunals to the single residual mechanism. As mentioned above, ad hoc and hybrid tribunals can be established, and terminated, in unforeseen circumstances. For instance, a tribunal’s mandate could prove to be politically controversial, or might terminate before the completion of its duties due to budgetary issues, as was the case with the STL. 

A trigger mechanism would allow the single residual mechanism to have control over which tribunals it would succeed, and under which circumstances. A trigger could be a numerical or percentage-based threshold based on the number of indictees prosecuted, which would be built into the legal instrument regulating the transfer of residual functions, such as the charter of the tribunal or the transfer agreement. 

Alternatively, the trigger mechanism could be an oversight duty given to an office or a committee to evaluate the unique circumstances of the transfer. The latter option could provide for more flexibility than a predetermined trigger, but could also lead to accusations of bias. 

A carefully planned and implemented transfer strategy would be key to ensuring a successful transitioning of cases from existing tribunals to a single residual mechanism.

4 – Choice of Law

What substantive and procedural laws would the single residual mechanism apply to fulfill its residual legal duties? The IRMCT example provides minimal assistance in resolving this choice-of-law issue since it combined the residual duties of ICTY and ICTR, two tribunals of purely international character with markedly similar substantive and procedural laws, both created by the Security Council under its Chapter VII powers. The subsequent tribunals have not followed this model and apply a mixture of domestic and international law.

One of the main goals of hybrid international tribunals is to reflect national and regional nuances. The ECCC, SCSL, and STL incorporate numerous unique features from their relevant national jurisdictions, from substantive laws to procedural rules, and even nomination and seat requirements for judges on the tribunal. Principles of equitable treatment would require the single residual mechanism to apply the same substantive law to an apprehended indictee brought before it that was applied to those prosecuted by the preceding tribunal. From a consolidation and efficiency standpoint, these diverging rules and requirements could be challenging to implement in a single residual mechanism. As a potential solution, the single residual mechanism could follow the approach of a U.S. federal court when it exercises diversity jurisdiction under the Erie doctrine – applying the substantive law of the state, while still applying its own bespoke procedural laws.

With respect to future tribunals, difficulties surrounding the choice of law may be temporary. Future tribunals could adopt the Rome Statute’s definition of core crimes and the single residual mechanism’s procedural rules, alleviating consolidation concerns. To address any diverging domestic laws, the single residual mechanism could recruit legal staff, including prosecutors, who are familiar with the substantive law of multiple tribunals. Nonetheless, how future ad hoc and hybrid criminal tribunals will evolve is an open question and a continuous challenge for a single residual mechanism designed to succeed multiple tribunals, including those which have not yet been established.

Political Considerations

Establishing a new single residual mechanism will require international cooperation during the mechanism’s formation, as well as during transfer of each tribunal’s residual functions. Depending on the tribunal in question, the required consents could include a majority of the Security Council (including its five permanent members), a majority of the U.N. General Assembly, or the individual States parties to the tribunals’ founding instruments. 

The political appetite for a single residual mechanism remains unclear. While the war in Ukraine has arguably invigorated international demand for accountability, the current deadlock and conflict within the Security Council may preclude any unified support for new endeavors in the field of international criminal law. 

At the same time, depending on how the single residual mechanism is funded, U.N. members may be forced to contribute to the budget of some tribunals that were once voluntarily funded, which could prove controversial. In fact, some tribunals, such as the ICTY and the ICTR, which were created through Security Council resolutions, have been funded by U.N. member States, through assessments calculated by the U.N. itself. Other tribunals, such as the ECCC and the SCSL, have been funded through voluntary contributions by member states. If the latter type of tribunals were to transition to a single residual mechanism which is not based on voluntary contributions but is instead funded by the U.N. through mandatory assessments imposed on member States, this would constitute a significant change in the funding model, and thus impose an additional financial burden on U.N. member States. 

The political sensitivity around the establishment of a single residual mechanism would also depend on the entity’s powers. An independent prosecutorial mandate could prove to be politically controversial. The single residual mechanism’s prosecutorial jurisdiction will track the prosecutorial jurisdiction of the underlying tribunals it consolidates. States may preemptively block the single residual mechanism if they oppose an underlying tribunal. For instance, Russia is likely to block any efforts that would increase the likelihood of the international prosecution of Russian citizens in relation to the war in Ukraine, even if those prosecutions could only occur after the single residual mechanism took on the prosecutorial mandate of a separate, underlying tribunal.

Obtaining consent from States parties to the tribunals’ founding instruments may prove challenging in certain situations. Sierra Leone has already consented for the RSCSL to share administrative resources with the IRMCT, which could suggest that it may be amenable to consolidation. Lebanon may similarly agree to the transfer of the STL’s residual activities to the single residual mechanism, as budgetary constraints have led the STL to cease investigative, prosecutorial, and residual activities. 

However, transferring the residual duties of hybrid international tribunals that are nationally integrated could see more pushback from the State in question. For instance, the Cambodian government may be reluctant to relinquish control over the ECCC’s archives, due to the role those archives play in framing the activities of the Khmer Rouge within the current political environment (see here for a discussion about the importance of preserving archives).

Finally, the idea of consolidation may receive pushback from existing tribunal staff and the international community. The cooperation of a transitioning tribunal staff is indispensable during the transfer of its residual powers, and tribunal staff may require assurance that a single residual mechanism can adequately support the victims, supervise the perpetrators’ sentences, and care for the records that had been their remit. Inevitably, however, consolidation of current residual mechanisms and future tribunals would lead to job loss for the tribunal staff, which could engender resistance from the States of the affected staff.

Administrative Considerations

1 – Archival Management

A number of administrative challenges must also be considered when establishing a single residual mechanism, some easier to resolve than others. Archival management, for instance, is a particularly technical challenge. Existing ad hoc and hybrid tribunals have diverging archival practices, with some tribunals, such as the SCSL, not yet implementing digitization of their archives. Digitizing and consolidating these sensitive files could be an expensive and lengthy project. Chain-of-custody, confidentiality, privacy, security, and longevity concerns would also have to be taken into account. However, the SCSL’s collaboration with the Dutch National Archives shows that the task is not impossible, and information sharing agreements can facilitate transfer of archival duties. Once a standardized archival system is created, future tribunals could follow the same system to facilitate the eventual consolidation with the single residual system’s archival system.

2 – Staffing and Budget

Other administrative considerations, by contrast, may not be so easily resolved. One challenge is that the consolidation of tribunals into a single residual mechanism would inevitably downsize the employed staff. In engagement with the U.N., and to avoid pushback from U.N. member States, care must be taken to ensure that such staff can be moved to comparable positions within the U.N. system. Another issue is maintaining a sustainable budget for the mechanism. A permanent single residual mechanism with prosecutorial powers would be expensive. As a possible solution, a single residual mechanism could adopt an “accordion model” that builds contingent funding into the single residual mechanism’s statute and allows it to expand – hire pre-vetted judges, prosecutors, defense counsel, and registrars – in the event of a trial arising.

Finally, the deep cultural, linguistic, and sometimes legal knowledge required of practitioners within any given tribunal places limits on the extent to which tribunal staff can be consolidated. Scholars and practitioners disagree on the extent to which each tribunal might require separate designated staff. The versatility of the ICC’s prosecutions demonstrates the ability of investigators, prosecutors, and judges to transition across factual sets without much previous regional knowledge. However, support from local staff and experts would likely be required to continue the residual functions of tribunals, especially if prosecutions continue.


As the symposium’s first post suggests, establishing a single residual mechanism is not a simple, purely administrative endeavor, especially if the goal is to consolidate all existing and future tribunals and mechanisms. Creating a single entity raises many thorny legal, political, and administrative issues with which the international community will have to wrestle with to go from a blueprint on paper to a brick-and-mortar institution. The final post in the symposium will outline three proposals for how a single residual mechanism could be structured in light of these considerations.