Testimony on facts
|Decision on Admissibility of Prosecution Investigator Evidence - 30.09.2002||
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The Trial Chamber denied admission into evidence of the conclusions drawn by a Prosecution investigator based on his summaries of written witness statements. See paras 16-17.
17. [...] [Those conclusions are] facts which the Trial Chamber is obliged to consider and in relation to which it must make its own findings before coming to the issue of the accused’s guilt in relation to them. That task does not require expertise beyond that which is within the capacity of any tribunal of fact, that of analysing the factual material put forward by the witnesses. Whatever expertise the OTP investigator may claim to have in relation to such a task, the Trial Chamber was entitled to decline his assistance in the very task which it had to perform for itself.
|Appeal Judgement - 28.11.2007||
NAHIMANA et al. (Media case)
212. […] Thus, while the report and testimony of an expert witness may be based on facts narrated by ordinary witnesses or facts from other evidence, an expert witness cannot, in principle, testify himself or herself on the acts and conduct of accused persons without having been called to testify also as a factual witness and without his or her statement having been disclosed in accordance with the applicable rules concerning factual witnesses. However, an expert witness may testify on certain facts relating to his or her area of expertise. […]
509. […] The Appeals Chamber recalls that the role of expert witnesses is to assist the Trial Chamber in its assessment of the evidence before it, and not to testify on disputed facts as would ordinary witnesses. […]
 Also, it should be recalled that an expert witness cannot pronounce on the criminal responsibility of the accused: see D. Milošević Decision of 15 February 2007, para. 11; Martić Decision of 13 November 2006, p. 5; The Prosecutor v. Casimir Bizimungu et al., Case No. ICTR-99-50-T, Decision on the admissibility of the expert testimony of Binaifer Nowrojee, 8 July 2005, para. 12.
 In this regard, see Rules, 66(A)(ii), 73 bis (B)(iv)(b) and 73 ter (B)(iii)(b).
 See supra IV. B. 2. (b).