In court, anyone taking the stand should have to expose their face.
Where does it say that, Wulfie?
Facial expression is a primary clue in determining the truth. It can be circumvented/exploited by someone who is a good actor or an accomplished liar so its not infallible in its own right, but it is still important. Facial expressions and reactions can give context that words alone do not.
I am glad you are aware of the limitation. The articles says that the victim was a Muslim born in Canada, it does not say if her parents were Caucasian or were from Middle East. But I am assuming that she is of Arab extraction, and not a Caucasian. If so, then the whole argument of facial expression is a washout. Non whites immigrants by and large tend to be inscrutable when it comes to emotion. Even when they show emotion, their facial expressions may not match our facial expressions.
So it is quite possible that in her case, either facial expression may not help at all, or even give wrong impression. E.g. suppose she is uncomfortable, fidgeting, nervous while giving testimony. Does that mean she is lying? Probably not. In her culture, it probably is not customary for a woman to appear in public, much less speak in public. Her unease, discomfort may be due to that reason and nothing more.
So I don’t buy the facial expression argument (unless the woman was a Caucasian).