What matters for assessing insider witnesses? Results of an experimental vignette study

Assessments of insider or accomplice witnesses are a major challenge in complex criminal cases, such as those of international crimes: war crimes, crimes against humanity, and genocide. While insiders are both important and problematic, little is known about how legal decision-makers determine to what extent such witnesses can be relied upon. This study, the first to experimentally study practitioner decision-making in this context, presents the findings of an online vignette experiment with former and current international criminal law practitioners (N  =  160). Quantitative analyses show that the assessments of the witness and the information quality are interdependent, hence, where an insider is considered not credible, the information they provide is perceived as less reliable as well, and vice versa. Furthermore, decision-makers tend to accord more weight to the quality of information rather than the quality of the witness, in line with jurisprudence analyses. The consequences for research and practice are discussed.