The parasomnia defence: expert evidence in criminal trials

Abstract

There are increasing numbers of defendants seeking to rely on the occurrence of sleepwalking or some other parasomnia in their defence to a criminal charge. Consequently this has become a matter for public concern, particularly in relation to sexual assaults committed after alcohol consumption. This study used ethnographic methods to understand how the expert witnesses assess the accused in these cases, and then present their evidence to the jury. It also looked at the two-way interactions between law and medical science, and the difficulties each field has with the other.
Sleepwalking in particular is an under-researched condition, with the basic phenomenology not fully explored yet. The experts must often rely on professional experience and give opinions, rather than relying on solid scientific evidence. Juries rarely return the special verdict, and victims are left dissatisfied by the incredible nature of the defence. The law pertaining to automatism and insanity is complicated and out of step with medical science. The Law Commission has recently examined this tricky area of law and recommended reform. The study concludes that the standard of expert evidence is generally good, although further work is needed to examine the specifics of how opinion and test results are presented to the jury. A number of recommendations are made about the standard of admissibility, legal reform and future directions of research.