![202304552 B1 - [2025] EWCA Crim 1051](https://backend.juristeca.com/files/emisores/logo_sHeHK8V.png){kind=logo}
The challenge to the forensic odontology evidence at trial
The challenge to the forensic odontology evidence at trial
As already mentioned, the prosecution wanted to adduce the evidence to show both that as part of the attack on him Alfie had been bitten, and to connect the applicant with the violence inside the caravan. Jack Benham also wanted the evidence of Dr Marsden to go before the jury. It was his case that he was nothing to do with the violence meted out to Alfie that night. Therefore, any evidence that some of the violence must have been inflicted by the applicant was beneficial to his case. Further, given his admission that he had bitten Alfie (although not hard enough to leave a mark) it was in his interests to make clear at trial that the only person who could be scientifically linked to a bite mark injury was the applicant rather than him.
The applicant’s challenge to the admissibility of Dr Marsden's evidence took place at a voir dire which took two days. Dr Marsden gave evidence for the prosecution. He set out his qualifications. He is a qualified dentist with a postgraduate qualification in forensic odontology. He holds a diploma in Forensic Medical Sciences and a diploma in Forensic Human Identification. He has practised as a forensic odontologist since 1989 and has twice been president of the British Association of Forensic Odontology. He has provided expert reports to both the prosecution and defence in over 150 cases and has given evidence in court more than 20 times.
It was his evidence that it was not always possible to determine whether a mark is a bite mark or whether the mark has been caused in some other way. He said that in many cases in which he had been asked to make such a determination he had been unable to do so and reported this back. However, in this case he had clear photographs of each of the injuries and was able properly to reach the conclusions he had reported on. He was able to give an opinion as to whether each of the disputed injuries was a bite mark. He said that he could exclude Jack Benham from having caused the injury to Alfie’s back because his dentition would not have permitted him to have left that mark. He did not claim that he could identify the applicant as having made it but rather that he could not exclude her as a candidate for having done so as her dentition would have rendered her capable of leaving the mark.
The evidence relied on by the applicant to challenge the reliability of expert forensic odontology evidence on bite marks came from Professor Iain Pretty, who gave evidence at the voir dire on her behalf. Professor Pretty is now retired from the University of Manchester. He has postgraduate qualifications in forensic dentistry. He is a fellow of the Royal College of Surgeons of Edinburgh and the Faculty of Public Health and former chair of the odontology section of the American Academy of Forensic Sciences.
Professor Pretty did not look at the images of the injuries to Alfie or at the impressions of the teeth of the applicant and Jack Benham taken by Dr Marsden. He did not engage with the facts or the particular evidence in this case either. Instead, it was his contention that there was no sufficiently strong scientific basis for ever admitting evidence of bite mark identification and bite mark comparison at trial. He said that a forensic odontologist should not be permitted to give expert evidence to the effect that a particular mark is probably a bite mark or that a particular individual's teeth can be excluded or not excluded from having made that mark.
He said that in the 1980s and 1990s there were miscarriages of justice in the United States caused or contributed to by defective forensic odontology expert evidence. He relied on a number of scientific reports which in his opinion undermined the integrity and safety of bite mark comparison evidence. In particular:
A report by the US National Academy of Sciences from 2009 which concluded that forensic odontologists should no longer be permitted to claim that the characteristics of any person's teeth are unique. That report recommended caution in respect of bite mark expert evidence; (Footnote: 1)
A draft report of the US National Institute of Standards Technology which was published on the 11 October 2022. In particular, a passage in it which reads: “Forensic bite mark analysis lacks a sufficient scientific foundation because three key premises of the field are not supported by the data. First, human anterior dental patterns have not been shown to be unique at the individual level. Second, those patterns are not accurately transferred to human skin consistently. Third, it has not been shown that defining characteristics of those patterns can be accurately analysed to exclude or not exclude individuals as the source of a bite mark”;
An article in the US Journal of Law and Biosciences from 2016 entitled “Forensic Bite Mark Identification: weak foundations, exaggerated claims”. That article criticised the practice of some forensic dentists of making a positive identification of someone as being responsible for having caused a bite mark solely from comparing the bite mark itself and impressions of the suspect’s teeth; and
Research from the University of Glamorgan. Twenty three forensic odontologists were each sent four sets of photographs of suspected bite marks to analyse and determine whether the mark was a human bite mark. Eight weeks later the same forensic odontologists were sent the same sets of photographs to be reanalysed in the same way. The aim of the exercise was to see whether all forensic odontologists reached the same conclusions based on the same evidence and whether the same forensic odontologist presented with the same evidence on different occasions would reach the same conclusions they reached on the previous occasion. Of the forensic odontologists approached, only three of them describe themselves as being very experienced. Of the rest, seven describe themselves as beginners in the field and ten were still students undertaking postgraduate degrees. There were disagreements among the twenty seven odontologists as to whether the mark was probably a bite mark. Some of them reached a different conclusion when asked to re analyse the photographs from that which they had reached when they were first approached to do so. Professor Pretty relied on this as evidence that the science of bite mark analysis was not sufficiently robust to be the basis for expert evidence at trial.
Professor Pretty was also critical of some of the methodology employed in this case. He said that it was difficult to draw conclusions such as those reached by Dr Marsden simply from viewing photographs of the marks; that there was a real risk that the shape of the mark on the skin was distorted because of the skin’s natural elasticity, and he pointed out that Dr Marsden’s conclusions were subjective in nature.
At the conclusion of the voir dire the judge indicated that he would admit Dr Marsden’s evidence. Later he gave a full written judgement explaining his reasons for doing so. The judge concluded that Dr Marsden’s evidence was relevant to a central issue in the case, namely identifying who inflicted injury to Alfie. He found Dr Marsden to be a highly qualified and experienced forensic odontologist who was capable of giving evidence of this nature. Although there was evidence of some controversy surrounding aspects of bite mark interpretation evidence, such evidence had generally been held admissible in the past. There was no scientific agreement that it was unreliable if used in the way in which Dr Marden had used it. Dr Marsden’s approach was in keeping with good practice. The judge found that the test for admissibility was satisfied and there was no basis to exclude the evidence under s78 Police and Criminal Evidence Act 1984.