Personal reflections of serving as an expert witness for a war crime

Expert testimony for a war crime trial is fraught with feeling of importance and anxiety. When in November 2022 I received the request from the state prosecutor Tom Laitinen to serve as an expert witness for a case regarding a war crime in Liberia during 1999-2003, I felt comfortable and even eager about it. Back in 2005 I served for five years as an accredited expert witness for the International Criminal Court but was never asked to attend because they relied very much on testimonies of Professor Willem Wagenaar. Since then, I had always wanted a war crime on my desk. I had worked with all possible crime types (school shootings, murders, serial rapes, kidnaps etc.) but with war crimes I felt that it does not get bigger than that. To put it in a perspective: The Second Liberian Civil War resulted in the deaths of over 50,000 people and the internal displacement of thousands more. It became worldwide famous for the widespread use of child soldiers, diamonds, President Charles Taylor and supermodel Naomi Campbell. So, when Mr. Laitinen called me, I didn’t think for more than few seconds and said: “Yes, of course I’ll do it.”

The atmosphere of war crime trial is somewhat unique and occasionally threatening to a witness. The proceedings may be held in closed sessions, the identities of the victims are protected, some witnesses receive death threats and, in some cases, witnesses have been murdered before or after testifying, even though some of them have been under the protection of the Tribunal. This particular case was out of the ordinary because the accused had been acquitted by the district court. Short after saying “Yes, I’ll do it” I started suffering from severe headaches due to the stress caused by thinking of the possible safety issues. The headaches lasted for three weeks. Finally, I consulted few colleagues of the safety issues, did some precautions, and got it resolved.

Despite of all the large-scale attention that a case like this has expert witness testimony in a war crime trial is a simple process. For a psychologist, the subject of the expertise in these trials is usually perception, memory, and trauma. Often there is no argument on whether the crimes ever happened because they are so widespread well known. A typical strategy for the defense is to claim that the accused was not involved in the crimes. So, they often run the case by arguing that the testimonies of the witnesses concerning the involvement of the accused is based on erroneous perceptions and false memories. Therefore, perceptual conditions (e.g. distance and lighting) in terms of facial recognition of the accused are of interest, as is the passage of time in terms of being able to remember and trauma possibly affecting how memories are presented.

There are often two types of witnesses in terms of perception. Those who have known the accused beforehand and those who have not. For a psychologist testifying on perception, witnesses who have encountered an unfamiliar perpetrator are of more interest. A witness who correctly identifies the unfamiliar perpetrator from a properly conducted line-up (either live or photo) ties the unknown perpetrator to the scene. Even if they would have difficulties in remembering some elements of the crime, they passed the lineup test. One can do this even after decades have passed.

There are also various types of witnesses in terms of memory. Some are consistent and remember details although such a long time has passed, others don’t. Some report a coherent narrative form one occasion to another, others don’t. At international criminal tribunals alterations in reporting of one’s memories from police hearing to presenting oneself at the tribunal have been “allowed” as long as they do not concern the critical crime related memories. Also, trauma affects many witnesses. It has an individual effect on how one remembers and presents oneself at the trial.

When I started working on the case over six months ago, I was somewhat surprised how much there is research on war-related trauma and memory. Research among veterans, refugees and holocaust survivors became extremely valuable source material. It provided a ground for understanding human memory in real life context. Of particular interest for me was to find research on how international Tribunals such as ICTY, ICTR and ICC have handled the witness perception, memory, and trauma issues. In the end, the amount of existing research made it relatively easy for me to write a statement containing 24 pages and over 100 scientific references. After working on it for over 130 hours (the source material consisted of over 5000 pages) I felt I really had given my everything. From the beginning I wanted to write an expert witness statement that could possibly be used on other war crime trials in the future. After all, same questions are raised after one trial and another.

Key factors of any experts witness statement are credibility, reliability, and validity of the opinions and the facts and logic upon which they are based on. For an expert witness this means answering questions honestly, telling the members of the court what one knows, how one knows it, and also what one does not know. ”Stay focused” would be my advice for anyone going to testify for the first time. This week, just before I was called in to provide my testimony at Turku Court of Appeals, I stood in the waiting area and for some reason memories of individuals who have said to my face, with a clear motive to disregard me (for a reason or another), that psychology has little relevance in the area of law or that the significance of my work is minor, came to my mind. Then I thought of professor Wagenaar. Sadly, at the age of 69 he passed away in 2011 and we never met. “I’ll tell them what you did and what you knew” – I thought referring to his classic study on the memory of the survivors of a concentration camp. With the effect that this type of research knowledge possibly has at the war crime trials, one can say that psychology can matter, I thought.


For more on work by Professor Wagenaar please see:

Wagenaar, W. A., & Groenewed, J. (1990). The memory of concentration camp survivors. Applied Cognitive Psychology, 4, 77-87.

W.A. Wagenaar (2009) Expert witness in international war crimes tribunals, Psychology, Crime & Law, 15:7, 583-596,


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