Post-Offence Conduct as Circumstantial Evidence of Guilt

Evidence of what an accused has said or done after an offence has been committed is often a vital part of the case for the Crown. This is circumstantial evidence that looks backward from what happened later to something that occurred before. The subsequent conduct may take several forms: for instance, flight, destruction of evidence, change of appearance.

R. v. B.(P.), 2015 ONCA 738 (CanLII), at para. 166. 
And sometimes that post-offence conduct can involve giving false evidence in court for the purpose of evading criminal responsibility.
The fact that a witness is disbelieved does not prove the opposite of what he asserted. The fact that a witness’s evidence is disbelieved on a particular point may have an impact on his overall credibility, but in order to prove the opposite of what he said some positive evidence is needed.

R. v O’Connor, 2002 CanLII 3540 (ONCA) at paras. 17-20;

R. v. Wright, 2017 ONCA 560 (CanLII), at para. 38.
Fabrication versus Disbelief

The law distinguishes between an exculpatory statement which is disbelieved and one that is found to have been fabricated or concocted to avoid culpability. A statement which is merely disbelieved is not evidence that strengthens the Crown’s case.

However, if the Crown can establish, through extrinsic or independent evidence, that an exculpatory statement was fabricated or concocted to conceal involvement in the offence, the statement evidence can be capable of supporting an inference of guilt.
R v. O’Connor
R. v. Wright, at para. 38.

Or as the Court of Appeal for Ontario succinctly put it as recently as this week:

It is an error of law to draw an inference of guilt from the disbelief of the accused’s evidence absent independent evidence that the accused person concocted a lie for the purpose of evading responsibility.

R. v. Sanchez, 2017 ONCA 994 (CanLII), at para. 37

So, for instance, a disbelieved alibi has no evidentiary value. A fabricated alibi can constitute circumstantial evidence from which an inference of guilt may be drawn.