Expert Evidence, Juries and the Search for Truth: A Case Study Analysis

One of the cornerstones of our society of which we are rightly proud is the criminal justice system. However, as with any system it is not without its flaws. Over the last 30-40 years there have been a number of miscarriages of justice involving flawed or misused expert evidence. This thesis attempts to answer the question “Does the situation with regard to the admissibility and presentation of expert evidence inhibit the courts from assessing such evidence in a rational manner, and does the system prevent the use and admission of expert evidence within the criminal justice system that could properly support the jury in reaching a just outcome?”

The selected approach is a mixed methodology utilising doctrinal analysis, socio-legal, and comparative law approaches within a case study framework.

The thesis reviews the Law Commission consultation paper and report on expert evidence, concluding that despite the failure to legislate the recommended statutory reliability test, the move to better control expert testimony by way of the criminal procedure rules (CrimPR) is a significant step forward, while noting that the failure to consider other aspects of admissibility represents something of a missed opportunity.

Consideration is given as to how the jury analyses evidence to reach a verdict, with discussion as to possible external influences and the effect of bias on the part of both the jury and the presenting experts. Consideration is also given to approaches which may better enable the jury and the court to both comprehend expert evidence and reach a rational verdict. The thesis posits that concurrent evidence and judge-only trials may provide mechanisms to better manage expert evidence before the courts.

In respect of eyewitness and earwitness evidence, it is argued that juries are in some cases being deprived of expert testimony as to the wide disparity between ‘common-sense perception’ and current science. As such, the jury is deprived of expert opinion that may better enable its decision-making. The recommendation is made that both the Turnbull direction given in visual identification cases, and the modified Turnbull direction given in the case of voice identification, need a more nuanced approach to better reflect the current situation. It is also recommended that with regard to earwitness testimony, not only does lay identification evidence require expert input, but the courts should follow the lead of the Northern Ireland Court of Appeal and mandate the use of more robust techniques for voice identification.

The penultimate chapter considers the possibility of polygraph evidence being used in criminal trials. There is evidence that a properly conducted polygraph is between 70% and 90% accurate. Evidence from the field of human psychology is that, in the absence of corroborating information, human beings do little better than chance when determining truth from lies. The thesis argues that it is illogical to ignore the possibility of using the more reliable form of evidence in favour of the less reliable, and that there is little English case law to prevent the use of polygraph evidence. It is argued that there is a route by which polygraph evidence could be bought before the courts and considers the possibility of legislation to this effect.

The thesis closes by making a number of recommendations for further study/reform.