Medical experts and the criminal courts

The quashing of Sally Clark's conviction for the murder of her sons Christopher and Harry has inevitably been followed by questions about the role of the medical experts, in view of their failure to disclose key evidence and the role such evidence played in securing her conviction.¹ The debate has been played out across the media, not least in the pages of the BMJ and on its website.²,³

Medical experts are called on daily to deliver their opinions in both civil and criminal cases. Critics have focused their attention mostly on criminal trials. The initial involvement of an expert may be through professional duties, as in the case of the forensic pathologist who performs an autopsy and then finds that evidence from the autopsy report is being used by the prosecuting authorities in a criminal trial. Other experts may be called on by the police or by the Crown Prosecution Service.

In the adversarial systems of law in the United Kingdom the defence is also entitled to seek appropriate experts. Expert witnesses are in a very privileged position as they may give opinion as evidence, unlike other witnesses who can only give evidence of fact. Whichever side experts are called by, their duty is clear—to give impartial and objective evidence for the court and not for the side that has called them. The defence may ask for an expert opinion and then choose not to use such evidence. If an expert opinion is to be used it must be disclosed to the prosecution. The prosecution, however, is under an obligation to disclose all its evidence to the defence.

We live in an era of evidence based medicine, and experts should base their opinion on solid evidence and not on intuition. Alan Moritz discussed the problem of substituting intuition for scientifically defensible interpretation in 1956.⁴ He said: “He [the pathologist] may be highly esteemed by the police and by prosecuting counsel because he is an emphatic and impressive witness. His prestige, together with exclusive access to original evidence, places him in an exceedingly powerful position in the courtroom.” A defence expert may be viewed by the jury as hired to say something that would help the accused. Moritz concluded the passage by saying that the stakes are too high to play hunches in forensic pathology.

Experts should be appropriately qualified and remain in their field. Concerns have been raised where an expert only ever appears for the prosecution or the defence and about experts who seem to be pursuing a sociopolitical agenda not based on objective evidence.

One of the major criticisms in the Sally Clark case was the use of the statistic giving a one in 73 million chance of a woman with Sally Clark's background having two “cot deaths.” This evidence was given by an eminent paediatrician but was roundly criticised by statisticians. Lord Justice Kay described the statistic as grossly misleading, although the first appeal court, aware of questions over the statistic, did not overturn the conviction. The main issue in the Sally Clark case was non-disclosure. The expert witness must include all relevant material, whether it supports or is detrimental to the opinion. The basic rule is that the prosecution must disclose its material to the defence. The microbiology results should have been in the pathologist's report, or their existence declared, whether they were felt to be important or not, so the defence could consider them.

The use of expert evidence in the legal system has been discussed in several reviews. Most recently Lord Justice Auld examined the role of experts.⁵ At present it is for the trial judge to determine who is an expert. The possibility of using experts appointed by the court was looked at but not recommended. Lord Justice Auld also rejected the argument that where a defence lawyer goes on a shopping expedition for a suitable expert all opinions should be disclosed to the court. This was on the basis that our current criminal trials are adversarial and the burden of proof lies with the prosecution.

The question of auditing expert medical evidence is an important one and has not yet been addressed. The courts are not the appropriate place for this. Many experts, including forensic pathologists, work in isolation. Individual cases are not reviewed before a report is prepared, although an annual audit of Home Office pathologists is undertaken in England and Wales. In forensic science laboratories, a second scientist validates each case. A second pathologist checks cancer diagnoses. No such check is routinely performed in autopsy work in England and Wales, despite the fact that the evidence may form the central core of a case that leads to life imprisonment.⁶ A second pathologist checking the work of a colleague should be routine in potential criminal cases. Forensic pathology services are currently under review in England and Wales, a region with few established centres. However, in these centres regular audit can take place, and we have instituted such checks on work performed in our centre. Clinical audit is now established. Medicolegal work should be similarly audited and subject to quality assurance.