At face value: Should a jury warning about the risks of assessing credibility from demeanour be mandatory in criminal jury trials?

In E (CA799/2012) v R [2013] NZCA 678 the Court of Appeal directly confronted the issue of whether demeanour warnings should be required in all criminal jury trials. Such a warning would alert a jury to the risks of using demeanour to assess credibility. While science has shown that demeanour is an unreliable tool for assessing credibility, the Court decided that a demeanour warning was not always required. As such, the law appears to be out of step with contemporary science. This article contrasts the traditional approach to the usefulness of demeanour evidence in criminal jury trials with a more modern understanding of its actual usefulness. Drawing on both social science and case authorities, this paper will critically evaluate the Court’s approach to this issue. The conclusion is reached that a demeanour warning actually should be mandatory in all criminal jury trials.