A Focus On: Forensic Psychiatry and the Expert Witness

A Focus On: Forensic Psychiatry and the Expert Witness


Image: Do Not Cross, Crime Scene. Reproduced from http://commons.wikimedia.org/wiki/File:Do_Not_Cross,_Crime_Scene.jpg


The “CSI Effect” has had a wonderful influence on our culture and the public’s perception of the justice system. If prime-time viewers take at face value the way television dramas depict how crimes are solved, then investigations require only a few tests, and professional investigative forces are aided by their savvy team members who are able to solve cases using meager evidence. This clash between entertainment and reality has led to courtroom juries expecting CSI-grade efficiency, and to prosecutors worrying that criminals will released without convictions if the case against them is not neatly presented.


With this in mind, we must look at a case that is not one typical of crime fiction, but instead one where the question is posed regarding the defendant’s mental state at the time of a homicide. The problem of presenting psychiatric testimony is compounded by the uncertainty and ambiguity in human behavior, and because of the lack of material evidence – smoking guns, microscopic fibers, or DNA. Additionally, the psychiatric expert witness was not at the crime scene or the arrest, and more often than not, a great deal of time has passed between the incident and the court appearance. Despite these quandaries, the system requires a psychiatrist to shed light on the question of bad versus sick.


What does the state of the science permit us to say in court? Perhaps more to the point, what does the law allow? A psychiatric expert witness can’t answer the ‘ultimate question’ of criminal responsibility, which is instead the duty of the jury or judge.


However, let us imagine there exists a gizmo that measures a person’s physiologic responses to a series of questions – and even correlates it with blood flow in brain areas. Can this contraption tell the court how the defendant was thinking or feeling at the time of the incident, or if they’re lying now? Repeatedly over the past one hundred years, courts have said “no”, and the use of a lie detector can only infer deception by analyzing the physiological responses to a series of questions. And even these are unstandardized.


So when will all the neuroscience research make it to prime time in the courts? The answer is coming, and there is already a budding area of “neurolaw”, as well as the use of fMRI in lie detection, although its use still has issues to be resolved. What is certain is that evidence of brain injury can mitigate against the death penalty. But reading minds? Stay tuned.


Kenneth J. Weiss is Clinical Professor of Psychiatry at University of Pennsylvania, Philadelphia, PA, USA.


Further Reading

1. Silva, J.A.(2009). Forensic Psychiatry, Neuroscience, and the Law. J Am Acad Psychiatry Law: 37(4), 489-502


2. Weiss, K. (2011). Head, examined: Clarence Darrow’s X-ray vision of criminal responsibility Journal of Psychiatry & Law: 39(4)


3. Eastman, N., Adshead, G., Fox, S., Latham, R., and White, S. (2012). Forensic Psychiatry. Oxford University Press



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