The legal framework for more robust forensic science evidence

1. Introduction

I express my gratitude to the Royal Society. It has played a key role in bringing together scientists and others interested in forensic science. By hosting the conference ‘The paradigm shift for UK Forensic Science’ it has provided a true forum to share developments and engage in discussion.

I wish to pay particular tribute to Professors Sue Black and Niamh Nic Daeid for their vision, their organization and their perseverance in getting so many distinguished scientists from all over the world together to achieve a paradigm shift in UK forensic science.

(a). Differing legal systems

There can be no doubt but that it is essential that we need to take forward and shape a common approach to the important issues facing forensic science and the law. That may be relatively easy for scientists, provided of course the work is funded and governed in a way that will drive forward change. For without finance and governance, little can be achieved.

But the work cannot depend on scientists alone, as forensic science must operate within the differing legal systems. The differences may at first sight seem a formidable obstacle, but I do not believe that they are. There are the well-known and different legal traditions, that of the common law and that of the civilian systems, by and large following either the French or German tradition of civilian jurisprudence. Each tradition has by the vagaries of history influenced most of the legal systems of the world.

It is now accepted that the work of comparative lawyers, whose discipline was based on finding differences, and the globalization of many legal concepts, particularly the rule of law as applicable to all governmental action and the right to a fair and open trial, have brought about a considerable narrowing of the differences. We have come a long way over the past generation in our approach to the differences between our systems.

Differences do remain, but they operate by and large as differing ways of bringing about (i) checks and balances in the investigative process and (ii) differing ways of fact finding. An example of the first is the duty of disclosure in a criminal investigation. All our systems recognize that it is an essential attribute of a fair trial that the prosecutor discloses to the defence any material that he has which might help the defence or show weaknesses in the prosecution case. In this jurisdiction, this basic duty has developed into a very far reaching obligation on the part of the prosecutor and on the part of experts deployed by the prosecution. We interpret the obligation as extending to all relevant material and have quite a wide concept of relevance. In our sister common law jurisdiction, the United States, exactly the same procedure operates more narrowly as there is a much narrower view of what is meant by relevance. In the continent of Europe, although this is a common obligation governed by the jurisprudence of the European Court of Human Rights at Strasbourg, the operation of disclosure in practice is generally governed by what is contained in the dossier and that is often very much narrower than what a prosecutor would have to disclose in England and Wales.

As for the second (differences in fact finding), some jurisdictions rely at all levels on fact finding by a tribunal of judges and others accord a greater or lesser role to the jury. There is again no clear division between the common law and civilian systems. Taking the jurisdiction of England and Wales, proposals have from time to time been advanced that difficult issues of expert evidence, particularly science, should not be left to a jury. The judge should hear the evidence and make a decision. In other systems, a single expert may play a great role. But even though we approach fact finding through a different prism, the ultimate responsibility must rest upon the judge or judges to ensure that the expert is asked the right questions, that the evidence given is fairly presented, that the accused is given a proper opportunity to challenge it and the decision on that evidence is logically explicable.

To that end, therefore, in whatever system forensic evidence is given, it is necessary to ensure:

• (i) that the expert evidence has a reliable scientific base;

• (ii) that the scientists giving evidence are themselves reliable;

• (iii) that the ambit of the expert's opinion is properly understood;

• (iv) that the system for collecting the evidence and safeguarding it during analysis provides clear continuity; and

• (v) that the expert evidence is explained to the judge or jury in a way that they can properly assess it.

(b). The centrality of sound forensic science

Before I turn to each of those themes, it is important to note how important forensic evidence is to confidence in a system of criminal justice, to the conviction of the guilty and to the acquittal of the innocent.

In October 2014, I began the Kalihser Lecture¹ (an important annual lecture delivered to criminal lawyers in England and Wales) by highlighting the centrality of sound forensic science to public confidence in criminal justice, ensuring fairness of proceedings and upholding the rule of law.

I do not think we can underestimate the force that forensic science has in a trial. That is because scientists are trusted. We live in an age where juries are being educated by TV crime drama to think that forensic science can solve everything and is infallible. It is essential that the science that juries are given is indeed robust enough to justify the second, if not the first, belief. A non-scientific scan of a week's television schedule reveals ten² different forensic-based crime dramas or documentaries, so it is no surprise that jurors arrive at court with what they perceive to be a level of knowledge and familiarity with forensic science.

They also arrive with a level of trust in forensic science. Whereas many witnesses may not be believed in a criminal trial, the scientist is seen as a person in whom trust and faith can be reposed. It is a high trust and our systems must ensure that it is not misplaced.

But, as been observed, forensic science is not simply relevant to a trial; it is highly relevant to public confidence in safety and in abating the fear of crime and crime reduction.

2. Ensuring expert evidence has a reliable scientific base

In dealing with the first of the five conditions I have set out, it is important to reference the major change that has happened in England and Wales over the last 10 years. In 2005, the House of Commons Science and Technology Committee called for reform in relation to expert evidence following concern arising from cases in the early 2000s.³ This call for reform was picked up by the Law Commission who, following consultation, produced an excellent and comprehensive report on expert evidence in criminal proceedings.⁴ One of the principal concerns of the Law Commission was that expert evidence was being admitted too readily and with too little scrutiny of its reliability by judges. Recommendations were made for the introduction of a statutory admissibility or reliability test (a proposal which the senior judiciary supported), a list of factors to assist judges in applying tests and the codification of existing law. These proposals aimed to provide a surer basis for the admissibility of expert evidence and to avoid the risk of the jury being confused and distracted by complex and conflicting accounts. As I explained in my Kalisher lecture, the Report has largely been implemented, even though no primary legislation has been enacted.

The Law Commission did, however, state that changes are

unlikely to provide a panacea. It is imperative that there be a broader context of change in tandem with the reforms…with safeguards and appropriate regulatory schemes … and a more critical approach on the part of some judges to the evidence placed before them.⁵

Let me therefore examine these two issues in turn, beginning with the role of the judges.

(a). The role of the judge: reliability

The Law Commission report stated that courts had adopted a ‘laissez-faire’ policy to the admissibility of expert opinion evidence and only rarely ruled that it was inadmissible on the ground of evidentiary unreliability.⁶ The Commission went on to say that courts tend to allow expert evidence to be admitted on the assumption that its reliability will be effectively challenged during cross examination or by contrary expert evidence by another party, or both. The Law Commission felt these were insufficient safeguards against unreliability. Indeed sole reliance on cross examination to expose questionable science seems at best brave and at worst foolhardy.

It is this issue of the Court willingness (or ability in some cases) to challenge robustly and be courageous in asking some uncomfortable questions of the science before it that needed to be tackled.

Key to the new approach are first the recognition of a test of reliability and second the factors that are to be taken into account in assessing reliability. In England and Wales, the condition has been stated as requiring a sufficiently reliable basis for its admissibility.⁷ The Scottish High Court of Justiciary has also re-stated recently a similar test in Young v HM Advocate⁸ as requiring that ‘it must be based on a recognised and developed scientific discipline’.

But what are the factors to be taken into account? The Practice Direction,⁹ mandatorily applicable and based on the Law Commission's recommendations, lists them as including:

• (a) the extent and quality of the data on which the expert's opinion is based, and the validity of the methods by which they were obtained;

• (b) if the expert's opinion relies on an inference from any findings, whether the opinion properly explains how safe or unsafe the inference is (whether by reference to statistical significance or in other appropriate terms);

• (c) if the expert's opinion relies on the results of the use of any method (for instance, a test, measurement or survey), whether the opinion takes proper account of matters, such as the degree of precision or margin of uncertainty, affecting the accuracy or reliability of those results;

• (d) the extent to which any material upon which the expert's opinion is based has been reviewed by others with relevant expertise (for instance, in peer-reviewed publications), and the views of those others on that material;

• (e) the extent to which the expert's opinion is based on material falling outside the expert's own field of expertise;

• (f) the completeness of the information which was available to the expert, and whether the expert took account of all relevant information in arriving at the opinion (including information as to the context of any facts to which the opinion relates);

• (g) if there is a range of expert opinion on the matter in question, where in the range the expert's own opinion lies and whether the expert's preference has been properly explained; and

• (h) whether the expert's methods followed established practice in the field and, if they did not, whether the reason for the divergence has been properly explained.

In addition, in considering reliability, and especially the reliability of expert scientific opinion, the court should be astute to identify potential flaws which detract from its reliability, such as:¹⁰

• (a) being based on a hypothesis which has not been subjected to sufficient scrutiny (including, where appropriate, experimental or other testing), or which has failed to stand up to scrutiny;

• (b) being based on unjustifiable assumptions;

• (c) being based on flawed data;

• (d) relying on an examination, technique, method or process which was not properly carried out or applied, or was not appropriate for use in the particular case; or

• (e) relying on an inference or conclusion which has not been properly reached.

Although there now appears to be common ground on the basic principles between the scientific and legal communities, they are not always easy to apply in practice. There is, for example, disagreement on whether reliance can be placed on unpublished research.¹¹ This is likely to be a more acute problem in England and Wales given the fact that much research is done by competitors; developments are not published and statistical databases may not be consolidated.

A judge also must always guard against the dangers inherent in any institutional consensus where old ideas are challenged or new ideas are advanced. The role of the judge in this respect is difficult and must proceed upon the confidence that a judge can place on the individual scientist challenging the established view.

(b). The role of the scientific community and a regulator

Although the judge has the role of gatekeeper at the court, there is an essential task to be performed by the scientific community in being prepared to validate the reliability of the underlying science.¹²

There are many ways for this to be done—through a more systematized approach to validation of underlying science by an established scientific body such as this Society or by a newly created transnational body.

A complementary, though in my view not an alternative, way is the role of the regulator. Sir Brian Leveson in his recent Review of Efficiency in Criminal Proceedings¹³ emphasizes the role of forensic science regulator in setting basic standards of quality. He comments that at its most basic level it should ensure minimum quality and security standards for accreditation of forensic laboratories. Sir Brian concurs with a view I expressed in my Kalisher lecture that although there are differing views on the question of statutory powers for a Forensic Science Regulator, such powers are now necessary to ensure, and if necessary enforce, compliance with quality standards. The power (or lack thereof) of the regulator is an issue also highlighted in the recent National Audit Office report to the Commons Science and Technology Committee.¹⁴

3. The reliability of the individual scientist who is to give the evidence

But even if the science is reliable, the expert must also be reliable—my second condition. Reliability is a problem and it is no use ignoring it.

(a). Registration and certification

Attempts have been made to address this problem in England and Wales through registration. From 1999 to 2009, the Council for the Registration of Forensic Practitioners attempted to ensure that courts could rely on experts by providing a system of registration. During its operation I had many discussions with the Council as to how its task could be fulfilled. First and foremost was the provision of finance. Second was the provision of a fair but not unduly burdensome system of peer review. Third was the ambit of the areas of expert evidence that had to be covered. Fourth there was the question of whether the court should insist upon registration or could admit evidence from an unregistered practitioner. These were all formidable difficulties, not the least of which was the first.

Since the closure of the Council, other bodies, including the Chartered Society of Forensic Sciences, have attempted to fill the gap.

The difficulties faced by such a body, as has been shown by what happened to the Council for the Registration of Forensic Practitioners, are formidable. For example, I doubt very much whether a private body could require more than a validation of the expert by the body. This would provide some degree of assurance to a court of the quality of the expert. But even if this was to be achieved, there would need to be assurance that the system of accreditation was robust and subject to regular independent scrutiny.

I agree, however, with the views expressed by Sir Brian Leveson, that a means has to be found of providing better assurance to the court that a witness called to give expert scientific evidence is credible.

An alternative, which certainly worked well in another sphere of expert evidence, is robust denunciation of an expert who does not live up to the highest standards. This has been done in a civil context where a judge can deliver his views on such an expert in a judgment. It is much more difficult to do in a criminal case, save possibly in an appellate system.

In relation to objectivity, Sir Brian calls, in his report, for greater emphasis to be put on the obligations contained in the Criminal Procedure Rules for the expert to provide not only assurance that the opinion has been prepared objectively with a view to the overriding duty of the court, but also to ensure that the court is informed of any significant change of opinion and the reasons.¹⁵ He recommends that the Criminal Procedure Rules Committee should consider the terms of the certificate required as part of the standard assurance every expert report must carry.

(b). Transparency

The transparency of the data put before the courts is an essential task for the judge. In R v Tyrone Wong,¹⁶ the importance of the requirements of transparency was highlighted. Transparency is important to ensure that in each case where an expert provider of a forensic opinion seeks to develop a new way of arriving at an opinion, that new way can be examined in open court applying the principles for admissibility—courts cannot apply the principles of admissibility if they are not made aware of the way in which an expert has reached his decision.

4. The ambit of expert opinion

Assuming the science is reliable and the expert a person of integrity, the third condition is the ambit of the expert scientific opinion. It is necessary to distinguish between two quite separate matters: (i) the issue that the expert scientist is addressing and (ii) the strength of his evaluative opinion.

(a). The issue that is to be addressed

In a criminal case, it goes without saying that the determination of guilt or innocence is a matter entirely for the tribunal that is trying the accused, whether it be judge alone or judge and jury. The role of the expert is limited to two matters. First, giving the basic scientific evidence necessary for determination of an issue that is relevant to guilt or innocence, and second, the provision of an evaluative opinion on the strength of that evidence. It is important, however, to emphasize that the role of the expert cannot be seen as in any way extending to the issue of guilt or innocence.

(b). The strength of the evaluative opinion

It is not necessary to say anything further about the giving of primary scientific evidence, but a word is necessary on evaluative evidence. It is, I think, nowhere disputed that a scientist is entitled and in most cases must express an evaluative opinion as to the conclusion to be drawn from the primary facts on which he gives evidence. However, it is very important to stress that a scientist cannot give evidence which is expressed in terms that his opinion supports (or does not support) the defence or prosecution case. His opinion goes to the likelihood of, for example, fingerprints being those of the accused or marks being made are marks that were made by a particular object. There can be no doubt that an expert can use his experience to give a judgment on such matters. More difficult, however, is the question as to the extent to which such an evaluative opinion can be based on a numerical approach. I cannot enter into that issue; I have given more than one judgment on the matter, but I do not really think if the judgments are read that there is any basic disagreement about the proper approach. It is an issue, however, that needs to be taken forward.

5. Continuity

I can deal with the fourth condition briefly. While it is accepted as axiomatic that the substance taken from the scene of a crime, or another location, must without doubt be shown to be the substance examined by the scientist and that there has been no contamination, I think we sometimes fail to appreciate the importance in the course of a trial of the assistance that a scientist who has visited the scene can give. In times of increasing financial stringency, it is important not to overlook the real value of attendance at the scene of a properly qualified forensic scientist.

6. Explaining the science so that judges and juries can understand it

If courts apply rigour to the reliability of the underlying science, if evidence is given by scientist in whom trust can properly be reposed, the ambit of the scientific opinion is properly defined, both to enable the courts to undertake those tasks and then to reach a just decision, it is essential that the fifth condition is met—that scientific evidence is understood by both the judge and the jury. Even if we have absolute confidence in the reliability of the science and the expertise and integrity of expert witnesses, we have to ensure that we continue to be able to use juries for trials where forensic evidence, even complex forensic evidence, plays a central role in the trial. This task will become even more acute as technology pushes boundaries and we are able to do things in new and novel ways.

It is a common experience in relation to all forms of expert evidence that experts will generally agree on most of the underlying matters and will disagree either about some particular aspect or the interpretation of what is common ground. For example, in relation to evidence on practices in the financial markets, it is the general experience that something in the order of 98 or 99 per cent will be in common ground between the experts; they will only disagree about one small, but critical, issue. In the development of our procedural rules, both in relation to civil and criminal proceedings, we have taken steps to ensure that the area in which dispute remains is clearly identified.

However, that does not obviate the need for the court, whether it be judge or jury, to have a proper understanding of those areas upon which the experts are agreed. In some cases, the way in which the matters upon which they are agreed has been properly explained by one of the experts. But that is not always the case. Furthermore, it is exceptionally wasteful of the time of experts (and hence an unnecessary cost) for the underlying and agreed basis of the science to be produced separately on each occasion.

Hence, following the practice developed in the Patents Court (where often the sums at stake are large enough for the court to require bespoke explanations of the underlying science to be provided), we have for some time been urging the provision of what are commonly known as ‘primers’ to enable the basic science to be properly set out in fields where evidence is common, in terms that can be readily understood by both judge and jury.

Faced with a common approach to the underlying science, it is far, far easier for the tribunal that decides the issue of fact to approach the real issue that divides the experts.

I have had discussions over the years with the former Regulator, and others, about the feasibility of producing standardized documents relating to the most popular areas of forensic science, presenting the basic science in an accessible, plain English format. This is what is done to great effect in the Patent Court and suitably adapted would make a great deal of difference in the criminal courts.

These ‘primers’ would be restricted to the areas on which there is consensus among the scientific community. They would, in my view, assist juries in understanding the concepts underpinning the issues in their case. There is of course a risk of oversimplifying scientific evidence, and that is not the intention: it is simply intended to assist juries with the basics, so that they can focus on the evidence in front of them. There would also be a challenge in keeping them updated, given the developments in science.

7. The ending of silos and tribalism: the need for good governance

It has been evident from what I have said that the basic problems I have discussed are problems common to every legal system. They arise from the much greater specialization and sophistication in the expertise that is developed in different fields of enterprise and of science. There is also, I think, a much greater risk of us living in our individual silos where those within each silo know a great deal about their particular area of specialization, but pay insufficient attention to working together.

We all share the desire to see a society where the risks from crime are less and, where crime is carried out, that the person accused is brought to justice by means of a fair trial. Although a primary duty rests upon those who play a role in the criminal justice system, and particularly the judiciary, it must be a shared endeavour by all of those involved including forensic scientists, where communication and dialogue are essential.

But discussion and dialogue will achieve little unless there is a firm way forward. That cannot be left to chance. For example, whether a particular issue in relation to forensic sciences comes for judicial decision is quite often a matter of chance: for example the case of Smith,¹⁷ as far as I have been able to discover, the first contested case of fingerprint evidence in England and Wales for many, many years. It was therefore chance that resulted in an area of expert evidence being examined in the courts in a way that demonstrated the need for change.

I therefore do not think that one can leave these issues to such chance, nor can the issues be left to scientists. I look forward, therefore, with great interest to the discussion moving forward and in particular hope that there will be funding identified which is necessary for progress to occur. Above all, what is needed is a structure of governance that will achieve results, for without that we will not make the progress that is essential.