Abstract
This article suggests that lawyers and judges may not understand the effects of their rules and procedures upon the production of evidence and its evaluation in criminal trials and appeals. Focusing on case studies involving the opinions of police officers and other investigators, as well as experts, it explains how applicable rules, procedures and safeguards did not produce, and appear incapable of producing, the effects claimed by courts. Drawing on scientific research – on cognitive bias and voice and face comparison – the article demonstrates how judges have enabled investigators to express their biased and speculative opinions, treated investigators’ opinions as expert (or special) without evidence of validity or ability, and encouraged jurors to make their own voice and face comparisons in the highly suggestive context of the accusatorial criminal trial. Courts have placed great reliance on trial safeguards, such as cross‐examination and judicial directions, trivialised the difficulty of voice and image comparisons and overlooked the likelihood that juror interpretations will be incurably biased, and that the same evidence will be unwittingly counted more than once.