R. v. Jolivet,  1 S.C.R. 751:
25 The general rule developed in civil cases respecting adverse inferences from failure to tender a witness goes back at least to Blatch v. Archer (1774), 1 Cowp. 63, 98 E.R. 969, where, at p. 65, Lord Mansfield stated:
It is certainly a maxim that all evidence is to be weighed according to the proof which it was in the power of one side to have produced, and in the power of the other to have contradicted.
26 The principle applies in criminal cases, but with due regard to the division of responsibilities between the Crown and the defence, as explained below. It is subject to many conditions. The party against whom the adverse inference is sought may, for example, give a satisfactory explanation for the failure to call the witness as explained in R. v. Rooke (1988), 40 C.C.C. (3d) 484 (B.C.C.A.), at p. 513, quoting Wigmore on Evidence (Chadbourn rev. 1979), vol. 2, at § 290:
In any event, the party affected by the inference may of course explain it away by showing circumstances which otherwise account for his failure to produce the witness. There should be no limitation upon this right to explain, except that the trial judge is to be satisfied that the circumstances thus offered would, in ordinary logic and experience, furnish a plausible reason for nonproduction. [Italics in original; underlining added.]
27 The party in question may have no special access to the potential witness. On the other hand, the "missing proof" may lie in the "peculiar power" of the party against whom the adverse inference is sought to be drawn: Graves v. United States, 150 U.S. 118 (1893), at p. 121. In the latter case there is a stronger basis for an adverse inference.
28 One must also be precise about the exact nature of the "adverse inference" sought to be drawn. In J. Sopinka, S. N. Lederman and A. W. Bryant, The Law of Evidence in Canada (2nd ed. 1999), at p. 297, § 6.321, it is pointed out that the failure to call evidence may, depending on the circumstances, amount "to an implied admission that the evidence of the absent witness would be contrary to the party's case, or at least would not support it" (emphasis added), as stated in the civil case of Murray v. Saskatoon,  2 D.L.R. 499 (Sask. C.A.), at p. 506. The circumstances in which trial counsel decide not to call a particular witness may restrict the nature of the appropriate "adverse inference". Experienced trial lawyers will often decide against calling an available witness because the point has been adequately covered by another witness, or an honest witness has a poor demeanour, or other factors unrelated to the truth of the testimony. Other jurisdictions also recognize that in many cases the most that can be inferred is that the testimony would not have been helpful to a party, not necessarily that it would have been adverse: United States v. Hines, 470 F.2d 225 (3rd Cir. 1972), at p. 230, certiorari denied, 410 U.S. 968 (1973); and the Australian cases of Duke Group Ltd. (in Liquidation) v. Pilmer & Ors,  A.S.O.U. 6529 (QL), and O'Donnell v. Reichard,  V.R. 916 (S.C.), at p. 929.