R v Hedges

Expert forensic odontological evidence concerning bite marks is admissible where it is relevant, needed, given by a competent expert and sufficiently reliable. Current science does not support positive identification of a biter from bite-mark comparison alone or claims that dentition is unique. It may nevertheless support an appropriately qualified expert’s opinion that a sufficiently clear skin mark is a possible or probable bite mark, and comparison of an unusual dental feature to include or exclude a suspect. Reliability is assessed in context, including data, methodology, peer review, competing expertise and limitations such as skin elasticity, movement and image quality. A cautious opinion that leaves the ultimate inference to the jury can satisfy the admissibility threshold.

The applicant and her partner were convicted at the Crown Court at Maidstone of murdering the applicant’s 18-month-old son. The prosecution relied in part on evidence from a forensic odontologist who classified injuries as possible or probable bite marks and could exclude the partner, but not the applicant, as the source of one mark.

After a two-day voir dire, Cavanagh J admitted the evidence and found no basis for exclusion under section 78 of the Police and Criminal Evidence Act 1984. The applicant renewed her application for leave to appeal against conviction, challenging the scientific reliability and admissibility of bite-mark evidence and the expert’s competence. The central issue was whether the evidence satisfied the requirements for admissible expert opinion.

The renewed application for leave to appeal against conviction was refused. The court granted leave for its observations on forensic odontology to be cited in future cases.

1. The applicable test, reflected in Criminal Practice Direction 7.1.1 and the common law as summarised in R v Dlugosz [2013] EWCA Crim 2, required the evidence to be relevant, necessary to provide information outside the court’s knowledge and experience, given by a competent witness and sufficiently reliable. The admissibility issue principally concerned reliability and competence.
2. The current science did not support claims that human dentition was unique or that bite-mark comparison alone could positively identify a suspect as the biter. Expert evidence making such claims would not be sufficiently reliable. That limitation did not prevent a qualified expert from assessing whether a sufficiently clear skin mark was a possible or probable bite mark.
3. Where a probable bite mark contained an unusual dental feature, an appropriately qualified expert could compare that feature with a cast of a suspect’s teeth and include or exclude the suspect from a list of potential biters. The expert could not make a positive identification. The significance of an inclusion or exclusion was for the jury to assess alongside the other evidence.
4. Reliability had to be assessed in context, including the data, methodology, peer review, competing expert opinion, established practice, image quality, skin elasticity and movement. The absence of peer review was a relevant factor but was not determinative. Subjective comparison was not inherently disqualifying where the expert’s expertise was the reason such evidence was required. Dr Marsden’s cautious methodology, qualifications, experience and treatment of the limitations satisfied the court that his evidence was sufficiently reliable and that he was competent.
5. The trial judge had heard the competing evidence at the voir dire and gave full reasons for admitting Dr Marsden’s evidence. His conclusion was not arguably wrong, and there was no basis for exclusion under section 78 of the Police and Criminal Evidence Act 1984. The conviction was not arguably unsafe, particularly since the case against the applicant did not depend on the bite-mark evidence alone.

• Court of Appeal (Criminal Division): The court refused the renewed application for leave to appeal against conviction, holding that the trial judge’s admission of the expert evidence was unimpeachable and that the conviction was not arguably unsafe: [2025] EWCA Crim 1051.
• Crown Court at Maidstone: Following a two-day voir dire, Cavanagh J admitted the forensic odontological evidence and the applicant was convicted of murder. No citation for the Crown Court decision is stated in the judgment.