Hedges v R – Clarifying the Admissibility Threshold for Forensic Bite-Mark Evidence

1. Introduction

In Hedges, R. v ([2025] EWCA Crim 1051) the Court of Appeal (Criminal Division), presided over by Dame Victoria Sharp P, refused leave to appeal against Sian Hedges’ conviction for the murder of her 18-month-old son, Alfie Phillips. The renewed leave application focused exclusively on whether expert bite-mark evidence—proffered by a forensic odontologist (Dr Philip Marsden) and admitted after a two-day voir dire—was sufficiently reliable to go before the jury. The Court not only upheld the trial judge’s ruling but set out structured guidance on when such evidence will satisfy the reliability limb of the expert-evidence admissibility test in England and Wales. Its detailed discussion is expressly intended to inform future cases, and thus lays down an important precedent on the cautious—but not exclusionary—approach to bite-mark testimony in criminal trials.

2. Summary of the Judgment

The Court affirmed that:

• The Criminal Practice Direction (CPD) 7.1 provides the governing framework: expert opinion is admissible where it is relevant, necessary, given by a competent witness, and “sufficiently reliable.”
• Concerns raised in the United States regarding bite-mark evidence primarily target positive identification claims premised on the “uniqueness” of dentition. Dr Marsden made no such claim; he merely excluded Jack Benham as the biter and could not exclude Hedges.
• Modern forensic odontology—applying probabilistic language (possible/probable/definite) and acknowledging limits—meets the reliability threshold if performed by a properly qualified expert who adopts a cautious methodology.
• Dr Marsden satisfied CPD 7.1.1(c)–(d): he was competent and his evidence rested on an adequate scientific base; criticism about lack of peer review, regulation, or skin distortion went to weight, not admissibility.
• Even absent the bite-mark evidence, the Crown’s case was strong; there was no risk Hedges was convicted solely because of the expert testimony.

Leave to appeal was therefore refused. Importantly, the Court authorised citation of its judgment precisely to guide future admissibility challenges of forensic odontology evidence.

3. Analysis

3.1 Precedents and Authorities Cited

• Criminal Practice Direction (CPD) 7.1 – sets out the four-limbed test for expert evidence admissibility. The Court’s application of CPD 7.1.2’s reliability factors is central.
• R v Dlugosz [2013] EWCA Crim 2 – re-affirmed that the court must be satisfied of a “sufficiently reliable scientific base” before admitting novel or contentious scientific evidence; cited as the governing common-law principle.
• U.S. Reports & Scholarship – although not binding, the Court referenced the 2009 U.S. National Academy of Sciences report, the 2022 draft NIST report, the 2016 Journal of Law & Biosciences article, and the Glamorgan repeat-analysis study to evaluate the broader scientific controversy.

The Court distinguished older U.S. miscarriages (where experts asserted uniqueness) from the limited, conditional testimony at issue here. Thus, far from excluding bite-mark evidence wholesale, it endorsed a nuanced, case-by-case approach.

3.2 Legal Reasoning

1. Relevance & Necessity – Identity of the assailant(s) inside the caravan was a core issue; lay jurors lacked the expertise to interpret bite-like marks.
2. Competence – Dr Marsden’s decades of practice, leadership roles, and conservative reporting style evidenced competence.
3. Reliability – The Court systematically addressed CPD 7.1.2 factors:
   • Data quality: high-resolution photographs; dental casts.
   • Methodology: BAFO “possible/probable/definite” scale; no claim of uniqueness; comparison focused on an unusual rotated canine.
   • Peer scrutiny: dearth of domestic peers was a weakness but not fatal; cross-examination and disclosure allowed adversarial testing.
   • Consensus & practice: modern odontology rejects definitive identification; Marsden’s evidence conformed to current best practice.
4. Balancing Exercise (PACE s78) – Potential prejudice was outweighed by probative value; limiting directions could manage residual risk.

3.3 Impact on Future Case-Law and Practice

The judgment sets a pragmatic benchmark:

• Conditional Admissibility: Bite-mark evidence is not per se inadmissible; its scope is restricted to inclusion/exclusion opinions, not identification.
• Methodological Transparency: Courts will expect experts to display candour about limitations (skin distortion, non-uniqueness).
• Expert Duty of Candour: An expert must cite contrary literature (the Court’s criticism of Professor Pretty underscores this).
• Prosecution Strategy: Prosecutors may rely on bite-mark evidence, but only where it is supported by high-quality imaging, clear features, and a conservative conclusion.
• Defence Tactics: Defence teams must go beyond generic attacks on the field; they should scrutinise the specific mark, methodology, and photographs to challenge reliability.
• Forensic Governance: The judgment could catalyse inclusion of bite-mark analysis under the Forensic Science Regulator’s Codes, and stimulate peer-review mechanisms.

4. Complex Concepts Simplified

• Voir Dire – A mini-trial (usually without the jury) where the judge decides if contested evidence is admissible.
• Forensic Odontology – The application of dental science to legal issues, including identification of human remains and analysis of bite injuries.
• “Possible/Probable/Definite” Scale – A British Association of Forensic Odontologists rubric:
  1. Exclusion: certainly not a bite.
  2. Possible: pattern could stem from teeth; alternatives cannot be ruled out.
  3. Probable: strongly suggests teeth; alternative explanation unlikely.
  4. Definite: no reasonable doubt it is a bite.
• CPD 7.1 – Criminal Practice Direction part governing expert evidence; courts must scrutinise relevance, necessity, competence, and reliability.
• PACE s78 – Allows exclusion of prosecution evidence if its admission would have such an adverse effect on the fairness of proceedings that the court ought not to admit it.

5. Conclusion

Hedges v R marks the first detailed appellate endorsement of a restrained, evidence-specific approach to bite-mark testimony in England and Wales. The Court confirmed that while the science cannot sustain positive identification claims, it can—where marks are clear and methodology transparent—aid a jury by narrowing the pool of potential assailants. Admissibility hinges on a confluence of relevance, expert competence, and methodological rigour, assessed through CPD 7.1 and common-law precedent. The ruling therefore balances safeguarding against junk science with the pragmatic need to place helpful specialist knowledge before juries, and is likely to be the touchstone for any future challenge to forensic odontology evidence.