PUBLIC confidence in the criminal justice system has again been shaken after the overturning of another murder conviction that had been secured with the help of unreliable scientific evidence.
Mark Dallagher was jailed in 1998 after a prosecution expert told his trial that an earprint on a window at the home of the victim, a 94-year-old woman, was certainly his. That evidence has since been discredited and new DNA evidence has implicated a different person. Mr Dallagher was cleared last month.
This followed the quashing of Angela Canning’s conviction for the murders of her two sons. The Court of Appeal’s judgment said that scientific evidence had come to light suggesting that the children may have inherited a genetic flaw.
All sudden infant death syndrome cases that have yet to come to trial will be reviewed personally by the Director of Public Prosecutions, such is the concern about forensic scientific evidence that the court described as being “at the frontiers of knowledge . . . where there is a serious disagreement about the cause of death between reputable experts”.
Confidence in the system had already been damaged by the announcement that old cases involving Alan Williams, the pathologist in the case of Sally Clark, will be reviewed. Mrs Clark, a solicitor, was freed from a life sentence after winning her appeal against conviction for the murder of two of her babies. At her trial Dr Williams had failed to disclose significant microbiological pathology results, denying the defence the opportunity of arguing that death may have been caused by biological infection.
Another cause for concern is the misuse of statistical evidence. Professor Sir Roy Meadow told the Sally Clark jury that the probability of two children dying from a cot death in a family was one in 73 million. The Royal Statistical Society (RSS) described this as an example of a medical expert witness “making a serious statistical error”.
There are other cases where the probability figure was also calculated without relating it to the specifics of the group being considered. In an American case quoted by the RSS, for example, the accused was convicted of arson at four properties. The probability of four fires was calculated as the fourth power of the probability of one fire. The figure had been produced without due regard to properties of a comparable type.
But what about other convictions that, like Mr Dallagher’s, have relied upon scientific opinion for which the evidence basis has since changed so that what was an accepted “fact” is now discredited? The truth is that it is simply not practicable to review all the cases where experts today would reach conclusions different from those that they would have reached in the past. These possible miscarriages of justice will remain buried.
Examples of such changes of scientific opinion were given by Christopher Hobbs, a consultant paediatrician, to a forensic science conference last year. “An example where experts have probably misled courts unwittingly for years is the ageing of bruises,” he said. He described texts that claimed to be able to age a yellow bruise, yet concluded that various studies had subsequently found that there was no evidence base for this. His second example was reflex anal dilation. In the first edition of a publication widely used in the courts, the sign was stated to be of significance if the diameter of the dilation was more than one centimetre. Yet in the second edition it had increased by almost double.
Improvements in technical evidence can also lead to different results over time. At the same conference last year Angela Gallop, a forensic scientist for 30 years, spoke about the advances in DNA analysis. She gave the example of a man charged in 2000 with a burglary. His DNA profile matched one obtained from the scene and which had been estimated to occur in one in 37 million people. He denied having been there and, fortunately for him, had an alibi. The police ordered a retest and this was performed using a newly upgraded form of analysis that looked at ten areas of DNA rather than just the original six. This demonstrated emphatically that he could not be the source of that DNA.
There is also the tendency for some forensic science experts to look for evidence that supports a particular theory of theirs, rather than be objective and impartial. To this list can be added the possibility of contamination of such evidence and the scope for scientists to place different interpretations upon the significance of it.
Despite these potentially serious shortcomings in forensic science evidence, the area is not a compulsory or usual part of a lawyer’s training and it is regarded by some as a special type of evidence, precise and irrefutable, beyond challenge or question. Only a decade ago, a study for the Royal Commission on Criminal Justice found that in three out of four cases scientific evidence went unchallenged and that more than a half of challenges were by cross-examination only.
It is to be hoped that the establishment of the Council for the Registration of Forensic Practitioners is a step towards filling this deficit. It is the first and only register of competent forensic practitioners in the UK that relies upon peer review and is able to provide the police, prosecution and defence with an accredited and able expert.
Helping lawyers to see the importance of when and how to consult a forensic science expert and to see that the expert’s competence has been independently verified is the next step.
Roger Ede is co-author of Forensic Practice in Criminal Cases, published by the Law Society in December 2003
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