by Alec Samuels
The expert witness may give his opinion because his expertise derived from study, qualification, knowledge and experience goes beyond the experience of the jurors, the ordinary men and women who came to court on the Clapham omnibus
.His function is to assist the jury to clarify and to understand the technical or complicated or difficult elements in the case as they assess and evaluate the strengths and weaknesses of the presentations by the prosecution and defence, and ultimately determine the issue, guilty or not guilty. The expert gives his opinion so that the jury can form their own opinion and decide accordingly. However, the expert is not entitled to express an opinion on the ultimate issue, that is for the jury and the jury alone. The expert must not be permitted to usurp or supplant the jury. We do not want trial by experts. The danger is that the jury may see an expert as so impressive, persuasive and authoritative that they take his opinion as the unalterable truth, as the answer to the ultimate issue. They must not think that he has given them the answer and all they need to do is to endorse his opinion.
The duty of the advocates and of the judge is to control the expert witness. The expert must be kept within his expertise and must justify his evidence Meadow v GMC  EWCA Civ 1390,  QB 462. The expert may not be fully aware of the niceties of the law of evidence, nor perhaps should he be expected to be aware. He is a psychologist or psychiatrist or doctor or forensic scientist or engineer or whatever. But he should be conversant with the Criminal Procedure Rules and the essence of his role. In a blatant case the judge may exclude the evidence as inadmissible. The advocates should carefully phrase the questions so that the answers are confined to the relevant expertise and do not stray into expressing an opinion on responsibility and liability, guilt or innocence. They should not induce the expert to give an answer on the ultimate issue.
In directing the jury the judge must make it clear what is the ultimate issue, what it is that the jury have to decide, and what is the role of the experts, namely to help them decide but not to decide for them. They must consider the expert evidence, but they are not bound by it.
All of us spend our lives identifying other people, so we do not need expert evidence on that matter. However, eye witness testimony has been the subject of much scientific research, which may be helpful. How well do we in fact accurately identify, as opposed to confusing resemblance with identity? We have all been mistaken by the “lookalike”. What should one look out for if claiming accurate identification? In looking at a photograph or CCTV picture what are the relevant features for identification? How about a video, possible disguise and facial mapping evidence? R v Stockwell (1993) 97 Cr App R 260.
Other forms of identification need expert evidence if in dispute, e.g. blood, DNA, fingerprints, footprints, shoeprints, ear prints, voice, handwriting. The margin of difference in these matters between A and B can so easily be very small and easily mistaken.
Is the confession reliable? Was the witness telling the truth?
The jury have to decide whether the confession by D, allowed in evidence by the judge, is or is not reliable. Or whether a witness was or was not telling the truth. It is not for the expert psychologist to say that the confession was reliable or unreliable, or that the witness was or was not telling the truth. But he can say that D or the witness is suffering from certain personality or psychological or psychiatric problems which in his opinion can lead to certain consequences, such as a propensity to lie, or to be vulnerable to pressure or suggestion or particular circumstances, e.g. when under stress, or under arrest, or in police interrogation, or in the witness box. The expert should not say that D or the witness was lying or was telling the truth. He should say that in his opinion all the indications for the reasons given are that D or the witness was or was not telling the truth. The expert does not assert or decide; he simply gives expert evidence, reasons based on his particular expertise in the matter of psychology of behaviour Pora v R  UKPC 9, paras 27-34.
Jurors, a number of whom will be parents, are likely to well understand the need to protect children, for example from the horrible pornography that pervades society, often directed at children. However, science has researched the effects upon children and expert evidence may be relevant and admissible and cogent DPP v A and BC Chewing Gum Ltd  1 QB 159, 164A-165B.
The law of criminal negligence is notoriously vague and uncertain R v Adomako  AC 1, R v Misra  EWCA Crim 2375,  1 Cr App R 21. R v Sellu  EWCA Crim 1716.
In a doctor manslaughter case the medical expert should not say that in his opinion the doctor was criminally negligent. What he can say is that in his opinion D acted contrary to good or proper medical practice, fell short of what is reasonably to be expected of a competent doctor, did not do what any competent doctor could and should and would have done in that situation. Drawing upon his qualifications and experience and the literature and his investigations the medical witness will seek to explain why in his opinion D fell short. Depending upon the circumstances, the sort of evidence the medical might give would be:
D did not examine the patient, or examine properly, or assess or plan the treatment. D was slow and inadequate throughout. D did not ask for blood tests, or did not examine them. D did not ask for a scan, or examine it. D did not listen to the nurses or the patient or the family. D left the case to an inexperienced junior. D did not consult a colleague. D did not prescribe the appropriate drugs. D did not offer a Caesarean section. D gave the wrong treatment. D was guilty of a serious error of judgment.
The judge will direct the jury on the law, and how to assess and evaluate the expert evidence. It is not for the medical expert to say that D was negligent, or grossly negligent, or reckless, or criminally negligent, but to show where, how and why D fell short, and death of the patient resulted.
Oliver Quick in a small research study found that because of the vagueness of the law the medical experts were confusing the civil law and the criminal law, engaging in subjective perceptions and moral judgments, enjoying the tactical forensic battle, and playing too prominent a role in the trial Expert Evidence and Medical Manslaughter, Oliver Quick (2016) 38 Journal of Law and Society 496-518.
Loss of self-control
Loss of self-control is a partial defence to murder, reducing to manslaughter, if a person of D’s sex and age, with a normal degree of tolerance and selfrestraint and in the circumstances of D, might have reacted in the same or in a similar way to D Coroners and Justice Act 2009 ss 54-56, R v Clinton  EWCA Crim 261,  QB 1. The test appears to be very much a jury question, with reference to normality, the objective approach, because jurors from their own life experience understand capacity for tolerance and self restraint, the desire for revenge, the “slow burn” of a woman in a violent or oppressive relationship. But there appears to be a subjective element in that the circumstances of D have to be considered. So it is possible to bring expert psychological evidence to say that as a result of examination of the circumstances the indications are that for reasons of mental illness or traumatic experience or low intelligence or whatever D suffered from a very low capacity for tolerance and self-restraint.
Expert medical evidence, usually given by a forensic psychiatrist or similar expert, is a practical necessity if in a murder case diminished responsibility for manslaughter is to be proved. The defence must prove on the balance of probabilities that D was suffering from abnormality of mental functioning which arose from a recognised medical condition which substantially impaired D’s ability to understand the nature of his conduct, to form a rational judgment or to exercise self-control, and provides an explanation for the killing as a cause or significant contributory factor Homicide Act 1957 s 2 as amended by the Coroners and Justice Act 2009 s 52.
The difficulties of application are immediately apparent. The expert does not think or diagnose or treat in these terms at all. The jurors very probably will not have any understanding or experience of abnormality of mental functioning, though they may have direct or indirect experience of mental illness or mental disorder.
The expert must present his report in professional terms. But he must also address the statute, and direct his opinion to the language of the statute, and the extent to which in his opinion the evidence of D’s state of mind does or does not fulfil the requirements of the statute. Words such as substantial, abnormality and impairment appear in the statute. They may or may not be psychiatric words. Nonetheless the psychiatric expert must translate his psychiatric language into layman’s language, ordinary language, as set out in the statute, for the benefit of the jurors. He may need to explain the significance of the medical history and diagnosis of D, of planning a killing, or the manner of the killing, of a brutal killing, of repeated attempts, of repeated killings, whatever may be psychiatrically relevant. Ordinary English words mean what they say, they carry their everyday workaday dictionary meaning. The meaning of a word can be elucidated or explained or interpreted by other words and phrases, and synonyms, and exemplified. But this process in itself can subtly change the emphasis, change the meaning. Intellectual semantic distractions should be avoided. So the expert should ultimately say whether in his opinion there is abnormality, whether there is impairment, and whether the impairment is substantial. Substantial means more than trivial, and less than total. Substantial lies somewhere on the spectrum. But more than trivial is not necessarily substantial, it depends upon the evidence in the case and the professional opinion of the expert, and is usually a matter of degree. Other words such as weighty, serious, significant, appreciable and important might be used, but at the end of the day the vital word is “substantial”.
In giving his opinion in this way the expert might appear to be giving his opinion on the ultimate issue, and in one sense he is. But this is unavoidable. He is, however, not saying that D is or is not guilty of murder or manslaughter. He is saying that on the evidence in his opinion D fulfils or does not fulfil the statutory requirements. R v Golds  UKSC 61,  1 WLR 5231, paras 27-42, especially 32, 36, 38, 39, 40, 41, 42.
The jury may or may not accept his opinion. There may be a difference of opinion between the experts. However, if all the experts agree then the jury should accept that evidence unless they have a very good reason for not doing so.
The role of the judge and jurors
The judges are keen to protect the independence and sovereignty of the jury, to curb any undue influence from the expert, and to keep him in his proper place. The jury must not be tempted to abdicate their responsibility and leave it to the expert. The judge must warn the jury not too readily to accept expert evidence. If the judge feels that the expert is straying beyond his role he may exclude the evidence, as happened to Professor Gudmusson in Pora; or he may be critical of the expert and weaken or even undermine him. The good and controlled expert does not impinge upon the ultimate issue, but he does assist the jury in their principal task, namely to determine or decide the ultimate issue.
© Alec Samuels, 2016