Safeguards For Psychiatry Expert Evidence In Criminal Cases

In criminal law cases, the discipline of forensic psychiatry shifts the focus from Who did it? to Who were they who did it? Through a series of judicial decisions and practice directions, the courts have established that before expert evidence can be admitted, it must have “a sufficiently reliable scientific basis”. In criminal trials, where the stakes for the accused and victims are so high, expert evidence’s credibility is crucial.

Prison psychiatry expert

Regarding trace evidence such as DNA, the following inferences must be established:

a) Two items share the same characteristics, and therefore, they probably come from a mutual source (normally one connected to the defendant),


b) Given that these items have a common source, conclusions can be made about the actions that led to one of these items being discovered where it was (Cook et al., 1998).

Regarding psychiatry expert evidence, this runs in reverse; clinical symptoms infer that past actions resulted from the condition that caused such symptoms.

How do psychiatrists assist in criminal cases?

Expert evidence consists of relevant information, likely to be outside the knowledge of a judge or jury, based on a reliable body of knowledge and experience, or for which there is a sufficiently reliable scientific basis for the evidence to be admitted.

In criminal law cases, although the accepted opinion is that mental illness and criminal behaviour are not linked, mental illness can lead to someone acting in a way that is outside of their normal behaviour. A Psychiatrist Expert Witness can assist legal counsel and the judge and jury in making their decisions with full knowledge of not only the defendant’s mental illness but also the way it presents and whether it was the mental illness that made the defendant commit the criminal act in question, as opposed to conscious intent.

Forensic psychiatrists can provide evidence in the following elements of a criminal law case:

  • Assessing fitness to plead
  • Assessing capacity to form the mens rea
  • Forming opinions about legal defences such as insanity and automatism
  • In cases of alleged murder, forming an opinion about diminished responsibility
  • Making recommendations for disposal (e.g. considering a hospital order)

What are the safeguards concerning the admission of psychiatric expert evidence?

Case law has developed several principles concerning the admission of psychiatric expert evidence, including:

Experts should not interpret evidence that jurors can interpret for themselves

In R v Turner [1975] QB 834, the defence psychiatrist inferred from his observations that the defendant had a particular “personality structure’. The psychiatrist stated that this “structure’ was consistent with the defendant’s statement that he killed his fiancée “in an explosive release of blind rage’. While accepting that the psychiatrist’s evidence was relevant, Lord Justice Lawton concluded that the evidence corroborating the “blind rage’ theory came primarily from the defendant’s own evidence, and knowledge of male reactions to female infidelity. The expert evidence was declared inadmissible because it would unduly complicate the jury’s task of assessing the plausibility of the defendant’s evidence. Given the psychiatrist’s expertise, it would give the defendant’s evidence too much weight.

Expert evidence regarding witness credibility should not usurp the jury’s role

In R v Robinson (Raymond) [1994] 3 All E.R. 346; [1993] 11 WLUK 175 (CA (Crim Div)), the defendant stood trial in 1992 for the rape of a 15-year-old girl with learning disabilities. An educational psychologist testified that the girl “could not adopt ideas from someone else. She would have difficulties taking them on board and relating them … She is not suggestible”. In this leading English decision on expert evidence of credibility, the Court of Appeal held that this evidence should not have been admitted because “the Crown cannot call a witness of fact and then, without more, call a psychologist or psychiatrist to give reasons why the jury should regard that witness as reliable’.

Wrapping up

Some of the key safeguards concerning the admission of Psychiatrist Expert Witness reports and testimony concern themselves with the principle that the jury must make their decisions based on the evidence placed before them. A psychiatrist provides valuable insight into the nature of any mental illness the defendant may be suffering and gives evidence as to whether, in their expert opinion, the defendant had a mental illness at the time the offence was committed. Still, they must not cross the boundary of usurping the jury’s role. This is a highly delicate balance to achieve and something the Psychiatry Expert Witnesses at Expert Reports understand and abide by at all times.

How can Expert Court Reports Ltd help?

Expert Court Reports provides expert witnesses and medicolegal court reports for solicitors, barristers and other agencies including the police, probation services, prisons, and third-sector organisations as well as private clients. To discuss any issues raised in this article, please call us on 01865 587865, email, or request a call by completing our online form.