The criminal standard of proof beyond a reasonable doubt applies to the essential elements of an allegation, not to individual pieces of evidence. As Sopinka J. states, speaking for a majority of the Supreme Court of Canada in R. v. Morin,  S.C.J. No. 80 at para. 36:
…the function of a standard of proof is not the weighing of individual items of evidence but the determination of ultimate issues. …The law is clear that the members of the jury can arrive at their verdict by different routes and need not rely on the same facts. Indeed the jurors need not agree on any single fact except the ultimate conclusion.
Sopinka, J. continues on to say, 41, that:
…The jury should be told that the facts are not to be examined separately and in isolation with reference to the criminal standard. This instruction is a necessary corollary to the basic rule referred to above. Without it there is some danger that a jury might conclude that the requirement that each …element of the offence be proved beyond a reasonable doubt demands that individual items of evidence be so proved.
- “…a chain is only as strong as its weakest link. If facts which are essential to a finding of guilt are still doubtful notwithstanding the support of other facts, this will produce a doubt in the mind of the jury that guilt has been proved beyond a reasonable doubt.” (Sopinka, J., in Morin, at para. 39)