What is the role of the expert witness in the trial and to what extent do such witnesses fulfil this role?

In understanding what expert witnesses do, one has to first establish the definition of an expert witness. An expert witness can be defined as “a person who can provide information and opinion from the body of knowledge that makes up their own expertise.” An example of an expert witness would be a psychologist. As a general rule laid by Lord Mansfield in Folkes v Chadd, “the opinion of scientific men upon proven facts may be given by men of science within their own science. In this essay, the term expert witness is going to be put under the microscope, divulging into the many aspects and rules of an expert witness and the opinion they give. A

In the Criminal Procedure Rule, it terms an expert witness a person who is required to give expert evidence for the purpose of criminal proceedings, including evidence that is to determine the fitness to plead or for the purpose of sentencing. For example one may call on a police officer that is experience in collision investigations may offer his expert opinion on how the accident transpired. There are also times when an expert witness is not required, where a judge or jury can form his or her own views and inferences without the help of an expert. Expert witnesses can be called to testify on a variety of issues, such as DNA analyses, engineering, architecture, handwriting, fingerprints, psychologists, pathologist, etc. “When knowledge of a technical subject matter might be helpful to a trier of fact, a person having special training or experience in that technical field, is permitted to state his or her opinion concerning those technical matters even though he or she was not present at the event.”

Expert witness will give an opinion of the facts that are presented in the relevant court case. It is known as opinion evidence. The opinion rule for this evidence is that the law makes sure that there is a line between a matter of fact, and a matter of opinion. Opinion evidence is generally seen as inadmissible, that the evidence the witness provides is not on their opinion of the fact, but that their testimony is based on the facts they have perceived. There are two exceptions to this general rule of opinion evidence: non-expert opinion evidence and a qualified expert in a specialized field.

Although most expert witnesses give their expert opinions on general topics at times, there are some cases where experts are called in for their expertise on unconventional cases. For example in the case of R v Browning, they brought in an expert of being able to recognize Renault 25s, the automobile. Also as in the case of Dallagher (2003), an officer who had a ten-year experience with ear prints was brought in to testify. In his testimony he stated matter-of-factly that the ear prints closely matched the defendant. By explaining the evidence to the court, based on the expert’s informed opinions, it helps the jury to draw certain implications to further help them with an outcome.

The role of an expert witness is generally to assist the jury in understanding the evidence presented at court, and lead the jury to make an informed conclusion. In the CPR 33.2,
(1) An expert must help the court to achieve the overriding objective by giving objective, unbiased opinion on matters within his expertise. (2) This duty overrides any obligation to the person from whom he receives instructions or by whom he is paid. (3) This duty includes an obligation to inform all parties and the court if the expert’s opinion changes from that contained in a report served as evidence or given in a statement.
The position an expert witness can have a tremendous affect on the jury’s final conclusion. Sometimes the opinions have a positive affect on the jury, and other times it can mislead the jury and sway them in the wrong direction.

Sometimes judges question the admissibility of expert evidence. The admissibility is typically based on the ‘Turner test’, which states, “an expert’s opinion is admissible to furnish the court with … information which is likely to be outside the experience and knowledge of a judge or jury. If on the proven facts a judge or jury can form their own conclusions without help, then the opinion of an expert is unnecessary. The fact that an expert witness has impressive qualifications does not by that fact alone make his opinion on matters of human nature and behaviour within the limits of normality any more helpful that that of jurors themselves, but there is a danger that they may think it does.” In R v Bonython, King CJ questioned whether the jury, without instruction or experience, could form a sound judgment of the matter of opinion without the help of a witness who is knowledgeable or experienced in that specific area. He also questioned whether the expert had the relative knowledge to actually be a witness in giving his expertise.

A judge has to determine whether a jury can come an informed decision without the help of an expert witness. In the case of R v Wood, the defendant was accused of rape but denied the allegations due to the fact that the complainant gave consent by having an orgasm. The Crown brought in an expert witness who was a medical examiner fielded in alleged sexual assaults. Although he was not comfortable giving an opinion based on an orgasm given under non-consensual intercourse, he explained what an orgasm was and how one would get an orgasm. A voir dire was held because the defence objected the medical examiner’s opinion evidence. When the examiner was cross-examined the expert did concur that an orgasm was usually associated with being pleasured, but also included later in his statement that it does not instinctively mean that the victim was actually enjoying the intercourse or consenting to the sexual act. This led to the judge ruling in favour for the evidence to be admitted. The judge’s reasoning was because the question was at first medically related (how the orgasm transpired) and the answer given by the expert was on that he felt the jury would not instantaneously known to the jurors in the trial. The defendant was convicted and then later appealed his case. He appealed on the basis that the expert was uncomfortable in giving evidence about non-consensual orgasms. The appeal was dismissed.

The Criminal Cases Review Commission bought the case back to court on the premise that there was a possibility that new, fresh evidence deemed the defendant’s conviction unsafe. The evidence pertained to the case of the second child. There were results from a microbiological test. The same pathologist that testified took body fluids from the infant during the autopsy, which isolated a form of bacteria. These bacteria could be proven lethal in any case. The pathologist seemed to have left this detail out of his report, and that he in fact tested the bacteria. In Clark’s appeal, several pathologists thought this to be abnormal for a pathologist to leave out such a crucial piece of information. And also the fact that bacterial infection of any kind could and should not have been excluded from the infant’s cause of death. The statistical analyses provided for the case was also a problem, the numbers were off. Because of this information that was left out by the pathologist, done purposefully or not, the appeal was allowed and the convictions were unsafe. The evidence against the defendant made her seem guiltier than she actually was. A similar case was seen in R v Cannings.

As a result of the O’Brien case, in the judgement it defined the limits where expert psychiatric evidence might be used: 1) The abnormal disorder should not only be of the type, which might render a confession or evidence unreliable, and there has to be a significant deviation from the norm shown. 2) There should be a history predating the making of the admissions or the giving of evidence, which was not based solely on history given by the subject, which pointed to or explained the abnormality.

In the case of R v Weightman, there was a mother who was charged with murdering her two year old daughter. The defendant stated that she left her daughter in the room and returned to find her dead with a plastic bag over her head. Following the initial investigation, she admitted to the police, her husband and to her probation officer that she in fact killed her daughter. The question now presented to this case was whether the confessions were given as an ulterior motive. The defendant was deemed competent and did not put forth a defence of diminished responsibility, so a request was made to determine whether the confessions could be false. The judge, with the reason being that the jurors might be influenced in a case where she suffered from no mental illness or an IQ below 70, denied this request for a psychiatrist. Naturally the defendant appealed on the basis that the judge was wrong in denying a psychiatrist, but the appeal was dismissed. The defendant was known to have a histrionic personality, which was seen as the reason to her rash confessions.