The Crown's duty to call material witnesses extends to expert witnesses whose first contact with the prosecution came through the informant, who are appropriately qualified, whose evidence is admissible and available, and whose expertise and impartiality are not in issue. The Crown cannot make tactical decisions to decline to call such a witness in order to gain the forensic advantage of cross-examination. Where the Crown's refusal to call a witness is compounded by improper cross-examination and misleading final address when the defence calls the witness, this may constitute a defect depriving the accused of a chance fairly open to him of being acquitted.
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