Medical diagnosis of legal culpability: the impact of early psychiatric testimony in the 19th century English criminal trial

Fast-paced developments in psychiatry, neuroscience and emerging neuroimaging technologies place continual pressure on the legal recognition of mental illness and disease across jurisdictional boundaries. Nevertheless, the Canadian legal definition of exculpatory mental disease in the context of criminal liability has remained largely static, sheltered from the immediate influence of medical theory and advancements. In order to effectively reflect on the intersection of mental health and criminal justice systems in this area, it is important to understand its historical development and the English common law origins of the current approach. Specifically turning to the early 19th century, documented history and accounts of early medical witness testimony on the mental state of the accused provide a unique opportunity to understand the initial collision between fundamental concepts of moral and legal culpability and new scientific understandings of mental function and disease. In this article, I suggest that early psychiatric testimony to the accused's mental state challenged the evolving criminal law of 19th century England to reconcile its restrictive definition of "insanity" with expanding scientific reasoning and accounts of mental disease. The trial of Edward Oxford, an attempted royal assassination case of 1840, is examined as a symbolic height in this conflict prior to the first common law pronouncement of the current approach in 1843. As debate continues on the role of medical advancement in the identification of exculpatory medical disorders in law, this historical perspective may serve as a touchstone in balancing the enforcement of legal culpability with our society's greater appreciation for mental illness.