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Chapter 27 OPINION EVIDENCE As a general rule evidence of opinion of witnesses is not admissible in evidence . It is for this reason that such questions like “What is your opinion?”, “What did you think about it?” are generally not allowed because essentially they call for the opinion of the witness. To this rule, however, there are two exceptions, namely, evidence of experts , and the evidence of non-experts on certain matters. Expert evidence The opinions of people skilled in a subject or point in issue, for example, handwriting, finger impressions, art or any science, are admissible in evidence (see s. 47 TEA). It is for this reason that it is perfectly proper to ask a doctor to give his opinion as to the cause of death of any person, or as to what instrument could have caused a particular injury. Usually there is no difficulty in identifying who, in law, is an expert. But situations do arise when it becomes difficult to say who is an expert. Whether a particular person is an expert or not will depend on the nature of the question at issue, and the intricacy of the science, art, etc. In the case of Gatheru s/o Njahwara v. Republic, (1954) 21 EACA 384, the Court of Appeal for Eastern Africa held that when a trial court has to form an opinion upon the question whether a home-made gun is a lethal barrelled weapon, it must have the assistance of expert opinion, and that such “special skill” is not confined to knowledge acquired academically, but also includes skill acquired by practical experience; and that where a witness’s occupation imports a prima facie qualification , in questions touching upon matters usually dealt with in his capacity, he can be treated as an expert whose opinion is admissible. Difficulties often arise in subordinate courts in cases involving such substances as cannabis sativa (commonly known as bhang) and the local spirituous liquor commonly known as “moshi”. Who is an expert in identifying those substances? The usual practice is to send such substances to a Government Chemist who examines the stuff and issues a certificate as to its identity. In line with Gatheru’s case, it has been held that a police officer with vast experience in cases involving such substances may well be treated as an expert for the pur- pose of proving or disproving that the substance is or is not what it is alleged to be (see Iddi v. Republic, (1971) HCD n. 203; Salum Haruna v. Republic, (1968) HCD n. 37; and Jumanne Juma v. Republic, (1968) HCD n. 304). If, however, the witness has experience in an unrelated field, say, photography , and is treated as an expert witness for purposes of identifying the make of an engine, he will not be treated as an expert in the make of engines (see Omari Ahmed v. Republic, (1983) TLR 52). There is one more important point which public prosecutors often overlook when dealing with expert witnesses. Before proceeding to ask an expert witness on the point in issue, it is essential first to establish that he is, in fact, an expert in the field. He should, therefore, be asked questions such as his qualifications, his occupation, his experience and so on. That must be done even if the public prosecutor and the court know who he is. It must be on the court record. If the expert has prepared a report, it is not enough to ask him to produce it. He should be asked to explain it in as simple a language as he can. Not everyone understands the meanings of such words as “spercarditis ” “subarachnoid”, “medulla oblongata”, etc. Besides, the bare opinion of an expert may sometimes be unconvincing. He must give reasons for his opinion. One more point: the mere fact that your expert has given an opinion which supports your case does not necessarily mean that your troubles are over. A court does not have to accept the opinion of an expert witness if it finds good reasons for not accepting it (see Fayed Hussein v. Republic, (1957) EA 844; and Hassan Salum v. Republic, (1964) EA 126). In the English case of Abinger v. Ashton, (1873) LR 17 Eq. 373, Jessel, M.R. observed at page 374: An expert is not an ordinary witness, who hopes to get his expenses, but he is employed and paid in the sense of gain, being employed by the person who calls him…Undoubtedly...

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