How expert witnesses can make or break trials

By Rod Vaughan

How should one view expert witnesses? Hired guns, out to make a financial killing? Or fastidious forensic scientists, totally committed to establishing guilt or innocence without fear or favour?

With the increased reliance on the testimony of experts in legal proceedings, not just in New Zealand but globally, the question is often asked. Their pivotal role in criminal and civil actions can make or break a case, often with groundbreaking ramifications.

In New Zealand, think David Bain, Mark Lundy, Teina Pora, Ewen Macdonald and George Gwaze, to name but a few high-profile criminal cases involving complex scientific and medical argument.

Forensics of a different kind have also played a major role in determining the outcome of a multitude of civil cases such as corporate fraud or negligence. The leaky homes saga, for one, has drawn heavily on experts in many fields.

To address the issues thrown up by the proliferation of expert witnesses, many of whom may give conflicting evidence during trial, LawNews sought the views of some of the key players involved in their selection, training and use.

In the first of a two-part series, we quiz lawyer Nikki Pender who established Legal Empowerment, an Australasian company that trains expert witnesses, and forensic science consultants Dr Anna Sandiford and Paige McElhinney of The Forensic Group.

How widespread is the use of expert witnesses in criminal and civil cases in New Zealand and has there been a significant increase in their numbers in recent years?

Anna Sandiford/Paige McElhinney

There has been an increase in the criminal arena. It may now be easier to find an expert. We have more than 200 in our database and can find an expert to help with almost any inquiry.

It may also be because barristers are discovering how helpful an expert can be in not only assisting in their understanding of the science but also in asking the right questions.

Many more resources and scientists are now employed in DNA than previously. Unfortunately, that means there has been a reduction in some other areas of expertise and we are losing valuable knowledge as people retire.


What are some of the most high-profile criminal and civil cases where expert witnesses have played a pivotal role?

Nikki Pender

If you want a dramatic historical example of how pivotal witness performance can be, I would recommend episode seven of the podcast A Perfect Storm.

The podcast itself is about the death of Azaria Chamberlain and the miscarriage of justice suffered by her parents, Lindy and Michael. Episode seven covers the criminal trial, with an emphasis on the performance of the expert witnesses. Read more.

Joy Kuhl, a forensic biologist called by the prosecution, claimed that samples taken from the Chamberlains’ car tested positive for foetal blood. Her evidence was pivotal as it allowed for the theory that Lindy Chamberlain had slit the baby’s throat in the front seat of the car.

However, Barry Boettcher, a blood expert called by the defence, was able to show that the tests Mrs Kuhl used to detect foetal haemoglobin were also used for detecting traces of iron, meaning they were likely to produce false positives. In his opinion, the samples were at least as likely to be traces of copper oxide – a compound that is prevalent in the Uluru area.

The defence was therefore able to establish at least a reasonable doubt, right? Well no – the Chamberlains were convicted. According to observers, that outcome was due directly to the performances of the witnesses.

Mrs Kuhl was a very experienced, confident witness who had the ability to simplify her technical evidence and present it like a compelling story. Professor Boettcher, on the other hand, was nervous; he sweated profusely in the witness box, struggled under cross-examination and was unable to condense the nub of his evidence or otherwise engage the jury.

Are there any cases where their testimony has caused you to question their competence and/or motivation?

Anna Sandiford/Paige McElhinney

Yes. There is a growing body of research into the effect of bias on forensic examinations.

We know some of these are simply just part of being human and without the appropriate counter-measures in place, unconscious bias can occur. What is more concerning is the instances where experts have commented on aspects that are outside their expertise. Prosecution and defence lawyers need to have the appropriate training or scientific knowledge to spot when this occurs.

We are in a unique position as we see hundreds of reports every year from experts in all different sorts of expertise from across New Zealand, the UK and, occasionally, Australia, Europe and the USA.

In our experience, American experts can start from a position of advocacy whereas in New Zealand, Australia and the UK there are guidelines and codes of conduct that govern and guide the role of the expert witness and these do seem to reduce the issues.

Despite that, we see bias and advocacy, albeit sometimes it is quite subtle.

Motivational reasons are difficult to determine but seem to vary from blatant bias, wanting to assist the prosecution regardless of the strength of the science (‘it would be great to get the bad guy’) to stepping outside of areas of expertise so as to get more work, or a desire to get involved in high-profile cases.

Assessing competence can be an issue. The court is expected to know enough about experts to be able to decide whether an expert is an expert.

However, it often takes one to know one and it can be helpful to do some research and test a person’s CV to see if they are actually qualified and experienced in the areas on which they say they are qualified to give expert evidence. We have seen and know of several experts who step outside their areas of expertise.

Nikki Pender

The duty of expert witnesses is to assist the court and they must be sufficiently independent that judges and juries can trust their opinion. Judges are not shy about criticising expert witnesses for being too partisan.

The biggest risk for expert witnesses is that they stray outside their circle of genuine expertise into areas about which they have a general, but not specialist, understanding.

Skilled cross-examination can put them back in their box, so to speak, but overly-confident witnesses have been known to give persuasive opinion evidence that has turned out to be inaccurate, even misleading.

Another risk is more of an unconscious bias that can develop when expert witnesses regularly act for one side.

One high profile case in the UK involved paediatrician, Professor Sir Roy Meadows. A lawyer, Sally Clark, had been accused of killing her two babies, who she said had both died from sudden infant death syndrome.

Professor Meadows gave evidence that there was only a one in 73 million chance of two cot deaths occurring in the same family, a probability he colourfully likened to the odds of backing the winner of the Grand National year after year.

Professor Meadows was not a statistician and his evidence was fatally flawed. He was subsequently disciplined by the Medical Council who struck him off although that penalty was later overturned on appeal.

Another example from the UK is Dr Waney Squier. She is a paediatric neuropathologist who used to appear regularly as an expert witness for the prosecution.

After becoming increasingly sceptical about the science used to establish shaken baby syndrome, Dr Squier became a regular expert for the defence, including in New Zealand. Unfortunately, despite best intentions, she is perceived to be too much of a crusader and her evidence tends to be discounted. She has herself faced disciplinary action for allegedly ‘over-egging’ evidence in court cases.

Is there an adequate pool of expert witnesses in New Zealand and, if not, why? And what have been the ramifications?

Anna Sandiford/Paige McElhinney

Most of our experts and independent laboratories are overseas. There is a huge expense in establishing an independent accredited laboratory which makes it cost-prohibitive for us to do it here in New Zealand.

However, modern technology such as video conferencing in trials means there is now no barrier to accessing experts. New Zealand is a small country and there is a correspondingly small pool of experts from which to choose. Forensic pathology is a classic case.

We have too few forensic pathologists in New Zealand for the workload so we often source experts from overseas. There are no forensic neuropathologists here, so they have to be instructed from overseas for both the prosecution and the defence.

Due to the small size of New Zealand and our two degrees of separation, it can also be necessary or preferable to instruct experts from overseas to avoid local conflicts of interest. Many experts overseas aren’t concerned about New Zealand expert [witness] politics and most probably won’t have heard of any of our high-profile cases. This reduces the risk of bias.

It has also got cheaper and less complicated in the past 10 years for an expert to give evidence via videolink. Covid-19 has made it easier for experts overseas to give evidence here.

Nikki Pender

In the criminal area, there is a recognised problem with our small market.

If you are a qualified forensic scientist specialising in DNA sampling, for instance, you are probably going to work for the ESR and, if called as an expert witness, will give evidence for the prosecution.

Defence lawyers are often forced to look outside New Zealand for a second opinion which is expensive and usually dependent on legal aid approval.

In the civil area, it really does depend on the obscurity or otherwise of the area in issue. For example, if the issue is about quantifying economic loss in a negligence claim, or valuing assets in a relationship property split, then there should be a significantly large group of professionals who could provide an expert report. But that pool narrows if you are looking for someone experienced in giving evidence in court.

But there will be some specialist areas in which there is insufficient local expertise. It will be interesting to see whether remote participation by witnesses is more common in a post-Covid world.

What attributes make a good expert witness? How do you prepare them for court?

Nikki Pender

Mana, poise and self-assurance. The archetype that I commonly use when training expert witnesses is one of ‘teacher’.

Their mastery lies in their ability to explain complex details in simple terms; the best expert witnesses can make even the driest of subject matters seem fascinating.

Because experience matters, grey hairs on an expert witness can be a boon. Conversely, a master nuclear physicist who looks about 12 can find it difficult to be taken seriously. In the latter example, we would spend some time working on strategies to overcome perception issues.

Expert witnesses also have to walk the delicate line between being paid to take a side while having a responsibility to be independent. That can be easier said than done and we often spend time unpacking the expert code of conduct and discussing or role-playing practical ways of reconciling any tension.

Anna Sandiford/Paige McElhinney

Being a good expert witness is different from just being knowledgeable in a certain field. You need to be a good science communicator as well as unbiased and accurate of course, but also willing to change your interpretation when faced with new information.

Most of our consultants have at least 10 years’ forensic experience. If they are not from New Zealand then I warn them that, certainly compared to the UK, the New Zealand cross-examination process is much more, shall we say, robust.

Sitting down to give evidence in NZ is also unusual for some overseas experts if they do give evidence in person. This was quite unexpected for the experts who attended the Bain and Lundy retrials, for example, as it creates an informality that isn’t present when standing to give evidence.

Understanding and working to the New Zealand High Court Code of Conduct for Expert Witnesses is critical. It’s about a personality type as much as expert knowledge. Some people are just not cut out to be expert witnesses and there is nothing wrong with that at all.

To what extent are people deterred from becoming expert witnesses because of the stress caused by the often-aggressive adversarial process?

Anna Sandiford/Paige McElhinney

There is still a perception that independent experts are working for ‘the bad guys’ rather than working for the courts. For a lot of experts who have worked for the Crown for many years, it takes a considerable mind-shift to see yourself purely as an essential part of the justice system. This is equally true for becoming a defence barrister.

Medical experts in particular can, in our experience, struggle with the legal process. First and foremost, unless they are specifically forensic experts, their roles are to treat people. Involvement in the adversarial process is very much at odds with that process and many have no desire to be involved in the criminal legal system.

Nikki Pender

In 2013, Emily Henderson and Fred Seymour of the University of Auckland’s School of Psychology carried out an extensive study of expert witnesses’ experiences of cross-examination in the criminal and family courts. Read more.

Their findings were rather sobering, some of which said:

The concerns expressed to us reflect longstanding issues with the court process and with lawyers.

Developing an awareness of the adversarial system’s philosophy and of the impersonal nature of cross-examiners’ criticisms is important to experts’ emotional survival in court and is another area where training should assist.

Collegial support is also very important but can be difficult to find for experts living in smaller locales or who know few others working in the courts.

For our part, one of Legal Empowerment’s chief aims is to equip witnesses with the knowledge and skills they need to give evidence. We use role plays to focus on cross-examination techniques and strategies for managing stress and giving clear, coherent evidence while under fire.

How objective and independent are expert witnesses and to what extent do some consciously or unconsciously become an advocate for the legal team that has hired them?

Anna Sandiford/Paige McElhinney

Scientists for both the Crown and defence view themselves as objective and independent. However, this depends on the information provided to them. Human beings are inherently affected by bias, whether knowingly or unknowingly, and steps must be taken to reduce its effects.

Training in bias familiarity and recognition is given overseas, in the UK for example, but New Zealand is a bit behind in that regard. More could be taught and learned about it.

Nikki Pender

Expert witnesses are required to be objective and independent and will usually strive to do so. However, misunderstandings about their role are common and many witnesses can come across as advocates. Sometimes the lawyers must take responsibility for setting stricter boundaries.

As tempting as it may be to have an expert on hand as part of the litigation team, too much familiarity with the case (and client) risks making the experts appear too partisan and can undermine their evidence.

Lawyers should also avoid briefing expert witnesses together unless it is strictly necessary. If nothing else, there is the risk of the evidence sounding too similar, as if the witnesses have been rehearsed or are speaking in unison rather than independently.

To what extent do lawyers shop around for expert witnesses who will say what they want them to say?

Anna Sandiford/Paige McElhinney

We see only the lawyers who approach The Forensic Group and they come to us for an unbiased assessment of their case.

We will summarise the findings in a way they can understand and tell them what the findings mean and whether they support the Crown or defence proposition.

If we receive a query ‘can you say x?’ we will assess all findings in the case and provide an unbiased assessment. There is the added advantage that the lawyer is prepared for how the Crown might use the findings at trial.

If a case is funded by legal aid, there is less likelihood that expert-shopping can occur as, in theory, a good argument must be made to legal aid as to why a further expert must be instructed. Some experts are hired guns and some lawyers will always use them because of that. However, I think that is becoming less common as transparency in the system increases.

Again, New Zealand is a small country, so news of biased experts tends to spread quite quickly. And in this era of recognised miscarriages of justice and establishment of the Criminal Cases Review Commission, there are more checks and balances available to the courts for assessing the expert-shopping process.

Nikki Pender

It would be rare in criminal cases. The prosecution has a duty to disclose, so any contrary opinion will be (or should be) made available to the defence. And while the defence has no corresponding duty, it is usually legally aided and subject to cost constraints.

It may be more common in civil cases, especially big-budget ones.

Discovery rules, to the extent that they still apply, require all expert reports to be listed although litigation privilege prevents them from being disclosed unless produced in evidence.

In the US, expert witnesses are often regarded as little more than hired guns who make large sums of money. Is there any evidence of this emerging in New Zealand?

Nikki Pender

I’m not aware of any such evidence. The US justice system is very different. There, experts are not required to be independent and can (and do) advocate strongly for the party who calls them.

Personal injury cases also make a difference. In New Zealand that area of law was displaced by the ACC system. The US and other jurisdictions which still allow personal injury claims often see these proceedings bogged down by expert evidence, with some medical practitioners working almost fulltime as professional expert witnesses.

Were we to reach a point where expert witnesses were causing imbalances or inequities in the justice system, we could adopt civil procedure rules similar to those that have operated in the UK since the Woolf reforms 25 years ago. These limit the ability of parties to call expert evidence without the leave of the court.

Anna Sandiford/Paige McElhinney

We need to make sure this does not happen. This relies on a body of experts who stand by the High Court code and represent the science for the court and not the instructing party.

While independent experts may be perceived to be only ‘picking holes’ in the Crown case, all parties have a duty to ensure the science before the court is correctly and fully explained.

In any industry you may have people who don’t play by the rules. It is up to all parts of the court system (Crown, defence, independent witnesses) to make sure the High Court code is complied with.

One way to address it is for the prosecution to challenge the witness and make sure he or she is qualified to comment. Again, because New Zealand is small, we have the advantage of everyone knowing someone. Experts acting as advocates are likely to be more obvious and therefore challenged.

Compared to prosecutors, are defence counsel disadvantaged when it comes to accessing expert witnesses in New Zealand? Is more funding required?

Anna Sandiford/Paige McElhinney

Funding is the defining factor in whether an expert is instructed. Ideally all cases should have access to expert witnesses.

Legal aid funding can be a challenge. However, we have been working with legal aid for many years now and spent time talking to them about the process for us. Our quotes are designed to meet the requirements of legal aid’s processes, so they get through the system more easily. The earlier in the trial process, the easier it can be to access funding.

By the time cases get through to total reinvestigation, such as Pora and Bain, hundreds of hours would have been invested free-of-charge. That time cannot be claimed retrospectively, which is why the CCRC is so important as it has its own budget, so lawyers and members of the public don’t have to do hours of work pro bono.

Unfortunately, there is a limited pot of money and funding must be prioritised.

More funding would always be welcomed as some areas of expertise are not being used as much as they used to be because the perception is that fingerprints and DNA can solve everything; they certainly advance many cases but there do seem to be times when other areas of expertise could benefit from investment.

Do you think the process for giving expert evidence should be reformed to make it less adversarial? If so, do you favour options such as pre-trial conferences where defence and prosecution experts agree on areas of agreement and disagreement, or do you prefer ‘hot tubbing’ where experts give evidence one after the other instead of being questioned days apart?

Anna Sandiford/Paige McElhinney

We have advocated in several instances for there to be open communication between experts, as there is overseas. There are still barriers to this – for example, defence barristers/experts cannot contact ESR scientists directly and questions can be addressed only if they come from the prosecution or police.

It would be ideal, and save the court time, if the Crown and defence scientists could formulate an agreed report for the court. Whether or not this is practical in terms of time is a different issue.

Hot tubbing has plusses because it gets experts done all at once rather than splitting them across a lengthy trial process; experts are possibly more likely to be reasonable when literally amongst their peers and it can be more explorative like the inquisitorial system.

The minuses are that the expert pecking order may come into play especially in a small country; stronger/appealing personalities may dominate regardless of accuracy of evidence; and counsel are not always keen because of loss of ‘control’ of the expert’s evidence.

Nikki Pender

I am a fan of hot tubbing, or concurrent evidence, as it is less evocatively known. The primary benefit is that it is easier for a decision-maker to crystallise the technical issues in dispute, understand the points of difference and seek clarification if necessary.

Expert witnesses tend to speak more highly of the process too. The decision-maker usually receives a joint report from all the experts after a ‘conclave’ or pre-trial conference.

The aim of the report is to set out the relevant issues and for each one to indicate whether the experts agree or disagree but not in a material way or disagree and the reasons why. The decisionmaker then gets to hear all the disputed evidence in one hit.

For insights into expert evidence in the health and safety field, you might be interested in attending our upcoming seminar on 28 October.



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