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Insider witnesses’ credibility and reliability: an empirical framework for international criminal justice

What factors impact insider witness credibility and reliability and how are they assessed in the investigations and prosecutions of international criminal cases? Gabriele Chlevickaite (VU, NSCR) conducted an extensive analysis of the jurisprudence of all the major international criminal courts and tribunals, as well as an experimental vignette-based survey. She is defending her PhD thesis on 29 March 2022.

This PhD defense is on Tuesday 29 March, 13:45 at the aula in the main building of VU University Amsterdam. Or join the live stream via youtube.com/VUBeadlesOffice.


International crimes cases, such as those of genocide, war crimes, and crimes against humanity, are of particular importance and gravity to societies affected by conflict and international community as a whole. At the same time, international criminal courts and tribunals (ICCTs) have faced increasing criticism regarding their fact-finding capabilities and practices, with several cases collapsing due to issues related to insider (accomplice) witnesses.

How could international criminal fact-finding be improved?

However, to date, surprisingly little is known about how legal practitioners decide whether to rely on a particular (insider) witness or not, i.e. how they assess whether an individual is providing truthful testimony. While prior research has shown that issues with witness testimony are common in the context of international criminal justice, with insider witness-related concerns particularly outstanding, we are yet to understand how witnesses are approached by the investigators and prosecutors at international criminal courts and tribunals, and with what consequences. Considering the criticisms levelled at the ICCTs regarding their practices, understanding the evidentiary foundations of international investigations and prosecutions is paramount to identifying whether, and if so, how international criminal fact-finding could be improved.

Extensive analysis of jurisprudence of all major ICCTs

This study aimed to answer the question what factors impact insider witness credibility and reliability and how are they assessed in the investigations and prosecutions of international criminal cases. Chlevickaite conducted an extensive analysis of the jurisprudence of all the major ICCTs: International Criminal Tribunal for the Former Yugoslavia, International Criminal Tribunal for Rwanda, and the International Criminal Court, as well as an experimental vignette-based survey. The jurisprudence was approached both qualitatively and quantitatively, as were the responses to the vignette study.

Reliable and trustworthy information

First, she looked at whether the judges across ICCTs have a particular method for assessing (insider) witnesses: is there an agreement over which criteria matters for determining whether the witness is providing reliable and trustworthy information? She found that by year 2012 (about 15 years into the functioning of the Yugoslavia and Rwanda tribunals), a general witness assessment framework, sharing elements across institutions, was in place, demonstrating cross-institutional learning and consolidation of practice. This framework features multiple insider-specific factors, including a ‘caution’ directive for assessments of insider witnesses, and pays attention to possible bias, personal motives, and other factors.

Lack of attention to witness competence factors

The second step was to check what this framework looks like in practice. In other words, do the judges use it, and to what extent? The analysis of judicial practice was based on 1,359 insider witness assessments in the ICTY, ICTR, and ICC trial judgments of 1996-2019. Importantly, the findings show that close to a half of the insiders at the ICC received a negative assessment outcome (47%), i.e. were deemed not trustworthy, with the numbers considerably lower at the ICTR (28.20%) and the ICTY (17.45%). Overall, negative rather than positive factors were mentioned more frequently and had more significant relationships with the assessment outcomes. Among quality considerations, those related to external validation (e.g., corroboration, contradiction) were more frequent than those related to internal quality (e.g., level of detail, coherence). Finally, in contrast to both prior research and assessment framework, an unexpected lack of attention to witness competence (e.g., memory, trauma, time-lapse) factors was found, showing that trauma is an experience that ‘belongs to’ the victims.

Complex picture of rather varied and inconsistent assessments

To bring the jurisprudence-based analyses to life, Chlevickaite conducted an experimental study employing vignette-based survey. 160 practitioners of international criminal law assessed insider witness statements of varying quality (e.g. some had more detail than others, some demonstrated more possible bias than others), and were asked to rate the statements and explain the score given. The analyses reveal a particularly complex picture of rather varied and inconsistent assessments across practitioners, suggesting that personal, professional expectations of the assessors matter in the outcomes of insider witness assessments, and that more consistency is to be desired from the perspective of predictable and reliable decision-making.

Improve practice in small steps

Finally, this study demonstrated that the task of insider witness assessments is multifaceted, and no single recommendation or framework so far appears to have ‘solved’ the issue. Throughout the thesis, recommendations are made to improve the practice in small steps, to bring the practice as best in alignment with both its own promises and current scientific knowledge.

Publication details and further reading

Chlevickaite, G. (2022). Insider witnesses’ credibility and reliability. An empirical framework for international criminal justice. NSCR/VU.


Promotor: Catrien Bijleveld
Co-promotor: Barbora Holá


Take a look at the factsheet Insider witnesses and international criminal justice: Empirical analysis, by Gabriele Chlevickaite.

Gabriele Chlevickaite MSc

PhD Candidate

Prof. Catrien Bijleveld LL.M.

Senior Researcher

Dr Barbora Holá LLM

Senior Researcher

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