R. v. McLean, 2022 MBCA 60, June 30, 2022, at paragraphs 43 to 45:
The conditions for a trier of fact drawing an adverse inference in a criminal case are:
1) An adverse inference cannot be drawn as punishment for a party exercising their legal right not to call evidence, even when there is a wholly unjustified explanation for the decision.
2) Because of the dangers of drawing an adverse inference, such as potentially reversing the burden of proof, the discretion to draw an adverse inference should be exercised with great caution and mindful of the division of responsibilities between the Crown and defence.
3) An adverse inference can only be drawn when there is not a plausible explanation for the non-production of the evidence.
4) The missing evidence must be relevant to a material issue. An adverse inference cannot be drawn as a result of matters unimportant to deciding the case or when there is already some evidence on the relevant point (even if it is of inferior quality).
(See Jolivet at paras 24-26; Lapensee at paras 42-45; and R v Maxie, 2014 SKCA 103 at para 38(iv)-(vi).)
If the conditions exist for the drawing of an adverse inference, whether a trier of fact will choose to do so will often be a function of the degree of the “special access” the party has to the evidence. The more the “missing proof” lies within the “peculiar power” of the party, the stronger the basis for drawing the adverse inference (Jolivet at para 27).
Precision about the nature of an adverse inference is important to keep in mind. An adverse inference is a tool to evaluate evidence, nothing more. When an adverse inference is drawn against an accused, the trier of fact must be mindful that the legal effect of such an inference is not proof of the guilt of the accused but, rather, the conclusion that, if the missing evidence was called, it would be unfavourable to the defence (ibid at para 28; R v NLP, 2013 ONCA 773 at para 74; and Degraw at para 32).