R. v. B.J., 2023 BCCA 166, April 21, 2023, at paragraphs 33 to 39:

There is a firm distinction between testimony that is found to be false, and therefore rejected, and testimony that is found to have been intentionally concocted or fabricated. The former has no evidentiary value and does not strengthen the Crown’s case. By contrast, testimony that has been deliberately fabricated can support an inference of guilt and can be used as circumstantial evidence for the Crown: Coutts at para. 13; O’Connor at para. 17; Beckett at para. 14.

The rationale underlying the rule was explained by Justice Doherty in Coutts at para. 15:

… If triers of fact were routinely told that they could infer concoction from disbelief and use that finding of concoction as evidence of guilt, it would be far too easy to equate disbelief of an accused’s version of events with guilt and to proceed automatically from disbelief of an accused to a guilty verdict. That line of reasoning ignores the Crown’s obligation to prove an accused’s guilt beyond reasonable doubt. By limiting resort to concoction as a separate piece of circumstantial evidence to situations where there is evidence of concoction apart from evidence which contradicts or discredits the version of events advanced by the accused, the law seeks to avoid convictions founded ultimately on the disbelief of the accused’s version of events.

See also Tessier at para. 89 and R. v. Iqbal, 2021 ONCA 416 at para. 54.

Thus, cases surrounding fabrication address a singular danger—the trier of fact, having rejected an accused’s exculpatory statement, will make an impermissible leap from disbelief to guilt: Tessier at para. 69; O’Connor at paras. 20–27. Distinguishing between disbelief and fabrication is thus “essential to ensure triers of fact properly apply the burden of proof in cases where an accused testifies”: Iqbal at para. 54 referencing Coutts at para. 15.

Though it may be logical to infer, from an accused telling a story that is not true, that they have intentionally fabricated it, “the law requires a further evidentiary step to safeguard against improper reasoning by the jury”: Beckett at para. 16; O’Connor at para. 21. In order to avoid convictions founded on disbelief of an accused’s version of events, the law requires that a finding of fabrication must be founded on evidence that is independent from the evidence which contradicts or discredits the accused’s version of events: Coutts at para. 15; O’Connor at paras. 21–23; Beckett at para. 16. In short, “the trier of fact cannot use the same evidence to find both falsity and concoction”: Beckett at para. 16.

The need for independent evidence was explained by Justice Ryan in Tessier:

[68]      It seems to me that the reason we look for independent evidence that the accused fabricated his story is two-fold. In the first place as my colleague Rowles J.A. has pointed out the reasoning is circular if there is no independent proof: “The weight of the Crown’s evidence admits of no doubt therefore the accused is not telling the truth. The accused is not telling the truth therefore the Crown’s case admits of no doubt.” In the second place, because the evidence that the accused has fabricated a story can be used as part of the Crown’s case against him, care must be taken in finding that the alibi was concocted. There must be a solid evidentiary base of fabrication. It is not unreasonable to demand that this evidence be found independently of the other evidence of the proof of the crime.

These principles often arise in the context of false alibis but that need not be the case: O’Connor at para. 18. Further, the cases also often arise in the context of disbelieved out-of-court statements but this too need not be so as “…the case law to this point in time does not draw a distinction between disbelieved out-of-court statements and disbelieved testimony.”: O’Connor at para. 27; Coutts at para. 15.

In Iqbal the court set forth the following useful framework for reviewing a judge’s use of an accused’s disbelieved evidence, arising from their in-court testimony (at para. 58):

a)   Did the trial judge disbelieve the appellant’s testimony?

b)  If so, did the trial judge also find that the appellant fabricated their testimony?

c)   If the trial judge found the appellant’s testimony was fabricated, was there independent evidence of fabrication capable of supporting that finding?

d)   If not, did the trial judge, despite the absence of independent evidence of fabrication, erroneously rely on the finding of fabrication as circumstantial evidence of guilt.