Legal versus non-legal approaches to forensic science evidence

Published date01 January 2016
Date01 January 2016
Subject MatterArticles
EPJ613470 3..28 Article
The International Journal of
Evidence & Proof
Legal versus non-legal approaches
2016, Vol. 20(1) 3–28
ª The Author(s) 2015
to forensic science evidence
Reprints and permissions:
DOI: 10.1177/1365712715613470
Gary Edmond
The University of New South Wales, Australia; Northumbria University, UK
In their attempts to determine the admissibility and probative value of forensic science and
medicine evidence, common law courts have tended to focus on considerations such as: the
formal qualifications and training of the analyst, the analyst’s experience doing the same or
similar things, the existence of a field, whether the evidence might assist the jury, apparent
partisanship and plausibility, the overall strength of the case and even the perceived need to
accommodate technological innovation. This article reviews conventional English approaches to
the admission and evaluation of expert evidence. It aims to contrast legal approaches to forensic
science evidence with the kinds of criteria being promoted by a range of peak scientific organi-
sations. This comparative exercise suggests that admissibility jurisprudence and legal practice
might be misguided, particularly in their attempts to regulate the comparison or pattern matching
disciplines. The article will suggest that courts have privileged the wrong kinds of heuristics in
their attempts to engage with scientific and technical forms of knowledge. More disturbingly, it
questions whether conventional admissibility standards, even in conjunction with trial safeguards,
provide jurors and judges with the kinds of information required to rationally assess much of the
incriminating expert opinion evidence routinely presented in criminal proceedings.
Expert evidence, admissibility, science, jury comprehension, trial safeguards, validity, opinion
The forensic sciences and the 18th century legacy
On certain matters, such as those of science or art, upon which the court itself cannot form an opinion, special
study, skill or experience being required for the purpose, ‘expert’ witnesses may give evidence of their opinion.1
The basic conceptual framework governing the admission of expert opinion evidence in England has not
changed in hundreds of years. This is unfortunate because the liberal admission of speculative, exaggerated
1. Folkes v Chadd (1782) 3 Doug 157 (Lord Mansfield CJ).
Corresponding author:
Gary Edmond, Expertise, Evidence & Law Program, School of Law, The University of New South Wales, Sydney 2052, Australia.

The International Journal of Evidence & Proof 20(1)
and unreliable opinions in criminal proceedings subverts fact-finding, may make trials substantially unfair,
places an insuperable burden on defendants (potentially compromising the burden and standard of proof)
and requires judges and jurors to assess techniques and derivative opinions in conditions that are not condu-
cive to rational evaluation (See Edmond, 2015a). For too long English courts have been insufficiently atten-
tive to the validity and reliability of forensic science techniques. For too long they have excused the failure to
evaluate techniques that ought to have been formally evaluated. This essay explains why conventional legal
approaches to forensic science evidence are not merely antiquated but poorly suited to the needs of modern
criminal justice.
The following section, headed ‘English admissibility ‘‘requirements’’’, reviews English admissibility
jurisprudence in order to compare rules and practice with the advice emerging from a range of peak sci-
entific and technical organisations, and reports prepared by senior judges, following protracted public
inquiries.2 Juxtaposition reveals substantial differences between the way legal institutions approach foren-
sic science evidence and the recommendations of scientists, engineers and doctors. While the essay is not
intended to suggest that courts ought simply to defer to the findings and recommendations of peak scien-
tific and biomedical organisations, there does seem to be a need to develop jurisprudence, rules and prac-
tices in ways that are likely to achieve long-standing and fundamental legal system goals (such as rectitude
of decision making and fairness), sensitive to budgetary constraints, institutional efficiencies and the cap-
abilities of participants.3 To maintain their public legitimacy, our courts should be engaged with scientists
and scientific knowledge. Simultaneously, they should provide persuasive justifications for persisting with
rules, practices and commitments that are inconsistent with the best advice from beyond the courts.4
The ensuing discussion builds on the findings and recommendations of a seminal report issued by a
committee of the National Research Council (NRC) of the US National Academy of Sciences (NAS).
Following a multi-year inquiry, involving submissions, hearings and a review of the available scientific
literature, the committee concluded that:
With the exception of nuclear 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. . . . The simple reality is that the interpretation of forensic evidence is not
always based on scientific studies to determine its validity. This is a serious problem.5
This passage targets forensic comparison evidence, sometimes described as the pattern recognition or
identification ‘sciences’.6 This essay is focused on non-DNA comparison techniques, specifically: latent
fingerprints, ballistics, tool marks, bite marks, tyre, shoe, foot, hand and ear prints, documents and hand-
writing, gait, as well as the use of images (for face and body mapping) and voice recordings, some insect
2. Especially, National Research Council of the National Academy of Sciences (2009) (‘the NRC report’); Lord Campbell (2011);
Expert Working Group on Human Factors in Latent Print Analysis (2012); Goudge (2008). For a critical overview, see Edmond
(2015b). See also Viscount Runciman (1993); House of Commons, Science and Technology Committee (2005) and Silverman
3. See e.g. Edmond and Roberts (2011). Contrast Ministry of Justice (2013).
4. An example might be the reluctance to impose Bayesian approaches to the interpretation of evidence on fact-finding in
adversarial trials. See e.g. R v Doheny and Adams [1996] 2 Cr App R 467, [1997] 1 Cr App R 369.
5. NRC (2009: 7–8, 87). In focusing primarily on techniques that involve comparison or pattern recognition, the infant death cases
and some prominent wrongful convictions have been omitted. Interestingly, in several appeals, such as R v Harris; R v Rock; R
v Cherry; R v Faulder [2006] 1 Cr App R 5, appellate courts were willing to receive additional evidence from highly respected
medical specialists and research scientists in an attempt to develop a more systematic institutional response to persistent
problems. See also R v Clark [2003] EWCA Crim 1020; R v Cannings [2004] EWCA Crim 1; R v Kai-Whitewind [2005]
EWCA Crim 1092 and R v Henderson [2010] EWCA Crim 1269.
6. The words ‘science’ and ‘expert’ are sometimes highlighted in order to draw attention to the fact that these terms are often
contested. In many instances we simply do not know if claims are scientific or if the forensic analyst possesses expertise doing
the specific task.

evidence, botanical and soil samples, ignitable fluids, paint, glass, fibres, hair and pollutants, to assist
with the identification of an individual or object.7
The NRC committee produced a deeply troubling assessment that should unsettle courts in all juris-
dictions, though especially England and Wales.8 For English courts preside over some of the most liberal
admissibility practices among advanced common law jurisdictions (See Edmond et al., 2013). In the
absence of evidence that contradicts the findings from the NRC report, or persuasive evidence that Eng-
lish trials and appeals consistently deal with these types of evidence effectively (i.e. presenting such opi-
nions in a manner that facilitates rational assessment), it might seem precipitous to discount the
substantive critique and epistemic implications of the failure to have formally evaluated many of the
techniques in regular use. As we shall see, relatively few of the findings expressed in the NRC and other
reports appear to be (well) known to English law. Many of the limitations are not disclosed, systemati-
cally explored or effectively conveyed in quotidian plea bargains, trials and appeals. There are few rea-
sons to believe they are understood, let alone taken seriously, by those asked to evaluate expert
When it comes to determining the admissibility (and probative value) of expert evidence in criminal pro-
ceedings, English courts have placed great store in trial safeguards and relied heavily on a range of heuristics
that are relatively simple to use and tend to facilitate admission and reliance. The kinds of heuristics (or
‘requirements’) in common use include: whether the forensic analyst has training, study or experience in
a legally-recognised ‘field’; a peculiarly legal incarnation of ‘reliability’; and perceived utility or necessity.
This essay endeavours to explain why traditional heuristics tend to be misguided and potentially mislead-
ing—providing only superficial insight into the value of forensic science techniques and...

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