The testimonies of insider witnesses are often key to prosecutions of international crimes, despite significant trustworthiness concerns. However, we know little about the practice of judicial assessments of insider testimonies, that is, which factors the judges consider relevant to relying on insider testimony. With this article, we set out to provide a comprehensive, explorative examination of the insider witness assessment factors used by the trial judges at the International Criminal Tribunal for the former Yugoslavia, the International Criminal Tribunal for Rwanda and the International Criminal Court in 1996–2019. By using multiple correspondence analysis, we show that the factors related to insider witness assessment outcomes are generally similar across the tribunals and tend to focus on the contents of the testimonies, with less attention given to credibility or competence concerns. This research constitutes the first systematic quantitative analysis and cross-institutional comparison of insider witness assessment practice at an international level.

Insider witnesses play an indispensable role in many international criminal cases. Despite often being essential for linkage evidence, the use of insider witnesses comes with a set of special concerns regarding their credibility, in turn casting doubt on the reliability of their evidence. This explorative empirical study aims to fill the gap in the scholarship and presents an analysis of credibility and reliability assessments of insider witnesses at the International Criminal Court (icc). It critically evaluates the use of such testimony to see if, how, and which factors relating to credibility and reliability affect the probative value of the evidence provided. The findings indicate that the icc judges put a lot of emphasis on factors such as consistency or detail of testimonies, while factors such as potential bias or questionable motivation of the witness surprisingly do not figure as prominently in ascribing probative value to evidence.

Accurate assessment of witness testimonies underpins judicial fact-finding at international criminal courts and tribunals (ICCTs). However, the lack of formal assessment criteria and uncoordinated methods, coupled with advances in the scientific understanding of the psychology of witnessing, calls for a re-examination of the judicial practice. This study critically evaluates the state of the art of witness assessments at the International Criminal Tribunal for Rwanda (ICTR), International Criminal Tribunal for the former Yugoslavia (ICTY), and the International Criminal Court (ICC), based on all the trial judgments issued in 1996–2019. The analysis results in a consolidation of this ad hoc, constantly evolving jurisprudence, into a framework that has been in development since the 1990s. The authors reflect upon the scientific validity of the criteria used throughout the analysis, based on up-to-date findings from psychology and criminology, and identify the areas that would most benefit from standardized procedures.

The international criminal courts and tribunals have heard thousands of witnesses in cases of extreme complexity and breadth. Their evidentiary record is overwhelming, with live witness testimony standing out as one of its defining features. Keeping in mind the arguments and policies of judicial efficiency and fairness, this article empirically examines the trends and patterns in viva voce witness numbers at the International Criminal Tribunal for the Former Yugoslavia (ICTY), for Rwanda (ICTR), and the International Criminal Court (ICC). We observe clear differences between institutions and individual cases, and discuss the underlying reasons for such divergences. As well as providing a general overview, we demonstrate the complex interaction between case-related characteristics, institutional and situational contexts, and the number of witnesses called at trial.