Guest post by Sarah Lucy Cooper, Senior Lecturer in Law at Birmingham City University and a Fellow at the Arizona Justice Project. Her PhD considers the influence of finality and legal process theory on American post-conviction relief mechanisms, against the backdrop of the American Innocence Movement.

Sarah Lucy Cooper presenting her research at the 2015 Western Society of Criminology Conference in Phoenix, Arizona.

In 2015, the British Journal of American Legal Studies will publish a special edition titled ‘Controversies in Criminal Law and Forensic Evidence: Views from the United Kingdom and the United States of America.’ The edition will present a comparative discussion exploring the relationship between criminal law and forensic science over the typical life-span of a criminal case, from crime scene to post-conviction relief. This blog post provides a brief overview of my paper that’s included in the special edition, which considers how, at the post-conviction stage, American judges respond to questions raised by scientific uncertainty within forensic evidence disciplines.


American courts have long embraced the idea that forensic identification disciplines―like fingerprint, tool-mark and bite-mark analysis―can engage in individualization; that is, identify the perpetrator of a crime to the ‘exclusion of all others.’ However, ‘indeterminacy’ (a term used in this context to refer to scientific uncertainty within a forensic discipline) has recently begun to manifest within these disciplines. This trend was bolstered by the publication of the National Academy of Sciences’ landmark 2009 report (the NAS Report), which concluded that ‘with the exception of DNA analysis… no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source.’

Petitioners have used the NAS Report’s criticism to shape newly discovered claims, arguing that it represents a ‘new’ shift in scientific opinion towards indeterminacy, which undermines their conviction. Appellate courts routinely reject such claims, however. In so ruling, these courts defer to lower court decisions that disqualify such criticism as newly discovered evidence, and tend to take the view that the NAS Report presents no ‘new’ facts given that it cites to older research and lacks specificity to individual cases. These approaches prove fatal under the high thresholds for relief contained within newly discovered evidence rules, which typically require proof that the new evidence (a) could not have been discovered prior to trial with the exercise of reasonable diligence; (b) is relevant and not merely cumulative or impeaching; and (c) creates a sufficient probability of a different result at a new trial.

This pattern of judicial decision-making showcases a judicial fidelity to notions of rationality, procedure, and predictability―key values of the legal process vision. The courts’ routine favouring of these values over substantive accuracy is problematic in the ‘Era of Innocence.’ Indeed, 49% of the current 325 post-conviction DNA exonerations are linked to unreliable forensic evidence, and it’s widely accepted that the criminal justice system generates factual errors. As such, this judicial practice raises important questions about the appellate courts’ institutional competence to address indeterminacy when shifting scientific opinion raises ‘new’ legal questions.

Institutional Weaknesses

American appellate courts suffer from a number of weaknesses when it comes to accurately assessing indeterminacy. First, appellate courts are used to assessing legal error. However, newly discovered evidence rules are primarily fact-based and require a factual assessment of the qualification, timing, quality, relevance, and impact of new facts. Consequently, they require courts to step outside of their comfort zone, particularly in the context of assessments relating to indeterminacy, as there’s a natural judicial tendency to avoid any deep confrontations with science.

Second, newly discovered evidence claims present vacuums in scientific knowledge. For instance, they may cite to the NAS Report’s findings that there’s a lack of scientific underpinning for tool-mark and bite-mark analysis. These vacuums pose (currently) unresolvable questions, such as: can a firearms examiner ever scientifically conclude there is a ‘match’ between a suspect weapon and suspect bullets? Can a tooth ever be uniquely linked with a bite-mark on skin? These are non-binary questions and the courts are poorly equipped to answer them because, as Meazell notes, ‘[w]hen a court is asked to resolve a question science itself has not resolved, it is simply unequipped to do so because legal values--and more particularly, the judicial process--do not employ the scientific method.’ Newly discovered evidence rules adopt this non-binary approach, requiring courts to determine whether the criticism of a forensic discipline is ‘new’ and whether it would have verdict changing capacity. They don’t present binary questions, such as whether a particular discipline has been criticised for engaging in individualization, which would be easier for the courts to accurately determine.

Third, the adversarial model prevents a full consideration of scientific issues because it encourages parties to ‘produce evidence favourable to their respective sides, regardless of the quality of that science,’ leading to a ‘battle of the experts.’ Fourth, judges generally lack scientific expertise and therefore are in a weak position to know what questions need to be asked in order to accurately test an empirical claim or evaluate scientific data.

Institutional Strengths

The appellate courts do have some institutional strength to review these claims. First, they have the competence to address these fact-based questions, as it’s their constitutional role to review the law. Thus, they have the institutional power to develop and engage in appropriate decision-making procedures that suit the task at hand, but also are sensitive to accuracy. The courts can also appoint independent experts, special masters, and specially trained law clerks, as well as convene the various actors needed to craft effective solutions to multi-dimensional problems such as those presented by indeterminacy.

Second, with the emergence of newly discovered evidence and actual innocence rules, there’s an increasing number of fact-based claims in appellate dockets. As such, judges should become more familiar (and competent) with science related fact-based assessments. Third, judges can engage in further scientific training. Judges are intelligent people with the capacity to engage accurately with technical issues. Moreover, the courts’ lack of a direct stake in the outcome of a case, and the respect they command, should enable judges to engage in objective, accurate, and thorough fact-finding.


The appellate courts must have a closer eye on accuracy. Courts cannot (and should not) be expected to conclusively resolve scientific uncertainty; however, neither should they―as a default position―hide behind procedural regularity to the detriment of accuracy, nor neglect their own institutional competence for providing the most accurate possible assessment of newly discovered evidence claims, based on shifting scientific opinion.

See Sarah’s forthcoming article ‘Judicial Responses to Shifting Scientific Opinion in Forensic Identification Evidence and Newly Discovered Evidence Claims in the United States: The Influence of Finality and Legal Process Theory’ in a special issue The British Journal of American Legal Studies entitled ‘Controversies in Criminal Law and Forensic Evidence: Views from the United Kingdom and the United States of America’ (edited by Cooper & Henneberg).