Witness proofing – or witness preparation – has been common practice at the ad hoc criminal tribunals but was prohibited in the first trial before the International Criminal Court (ICC) (the Lubanga case). The ad hocs have robustly defended the practice, claiming that it assists the efficient presentation of evidence and enhances the truth-finding process. This article examines the way in which the ad hocs have allowed the process to become an integral feature of their procedural regimes without sufficient examination of these apparent merits. The ad hocs appear to have accepted that prohibiting the parties from rehearsing, practising, and coaching evidence was in the interests of justice, but yet – in the uncritical acceptance of the benefits of proofing – have sanctioned practices which are impossible to distinguish. The Lubanga case represented a welcome attempt by the ICC to examine proofing and its attendant risks and, for the reasons outlined in the article, the chambers arrived somewhere close to the right decision.

This article examines the analytical framework and key arguments used by K. Ambos to conclude that witness proofing is neither a legally permissible nor necessary useful practice before the ICC in his reply to ‘Witness Proofing in International Criminal Tribunals: A Critical Analysis of Widening Procedural Divergence’. Contrary to Ambos, the article argues that witness proofing cannot be both acceptable at the UN international criminal tribunals and per se inappropriate at the ICC, given the ICC's procedural regime allowing for trials to be conducted in a form almost identical to those of the UN tribunals. A related argument is that the practice of witness proofing is not prohibited in the law governing the ICC, even if not provided for. Further arguments conclude that reliance upon spontaneity of a witness in court as a guarantee of reliability is misplaced, that the merits of national practices are irrelevant to the overall analysis, and that international judges are competent to manage the negligible risks associated with witness proofing.

This paper was written at the request of the LJIL editorial board as a reply to the article by Karemaker, Taylor, and Pittman published in the previous issue. It is argued that their position starts from incorrect assumptions and that their overall assessment of proofing is flawed, especially with regard to the risks for fair trial. As to the law of the international tribunals it is acknowledged, however, that there is a structural and normative difference between the ICTY (as the most important ad hoc tribunal) and the ICC. While the former still follows, despite some normative changes, a predominantly adversarial procedure, the ICC Statute provides for a mixed adversarial–inquisitorial procedure. Such a procedural model is not compatible with the adversarial origins of witness proofing and it is therefore not surprising that the ICC Statute does not provide for this technique. As a consequence, at the ICC proofing is neither legally admissible nor necessary.

Witness proofing – or preparation – is an adjunct of the adversarial criminal trial process. It is also a common practice at the UN international criminal tribunals, where it has been repeatedly challenged, analysed, and endorsed. Recently, a trial chamber at the ICC prohibited the prosecutor from proofing witnesses, seemingly calling upon the institution, at an early stage, to break with the established practice of proofing at the UN international criminal tribunals. This article examines witness proofing in international criminal procedure with the aim of describing and weighing its relative merits, and arguing that proofing – as practised at the UN international criminal tribunals – appears to be a better modality for enhancing the efficiency, integrity, and legitimacy of the truth-seeking function of international criminal trials than does prohibiting the practice.