Expert matters: Body of Knowledge: Expert evidence and the limits of 'specialised knowledge'

On 17 September 2008, an armed robbery occurred at a hotel in Sydney’s Northern Beaches. CCTV cameras recorded images of one of the offenders (‘Offender One’), whose identity was obscured by clothing covering his entire body and face. Police later arrested a man (‘the accused’) who had DNA and other circumstantial links to the offence, and whose appearance matched the (vague) descriptions provided by witnesses.

At trial, the key evidence led by the prosecution was given by Professor H, an expert in anatomy and anthropology, who compared the physical traits of Offender One with the accused. Professor H noted that statistical measurement of Offender One’s body was impossible because of the camera angle and low image quality. Rather, a comparison had to be made based on a qualitative judgment. For his report, Professor H had first viewed the CCTV recording and noted the physical characteristics of Offender One, describing him as:

"… an adult male of ectomorphic (thin, 'skinny') body build" … [t]he shape of the head is clearly dolichocephalic (= long head, elongated oval when viewed from the top) as opposed to brachycephalic (= short head, nearly spherical) …"

Professor H then analysed a video of the accused moving around in custody and described him as:

"… an adult male of ectomorphic (= slim) body buil[d] ... His skull vault is dolichocephalic when viewed from the top. Comparison of lateral (side) and front views of his head also indicates the head ... is long but narrow …"

The prosecution, wary of submitting evidence likely to be struck out, omitted this ‘high degree of similarity’ assertion from their case, but still included the less equivocal statement that Professor H couldn’t identify any distinguishing features. In closing, the prosecutor told the jury:

“[W]hen [Professor H] assessed the [appellant] from the known images he found all those characteristics to be the same. ... I'd suggest that you would accept his evidence as being of assistance to you, because it's reliable science and it is something that he can explain, even though you may not be able to see all of the things that he's been able to see." 

At trial, the defence objected to the inclusion of the report in evidence, arguing that it was inadmissible under the Evidence Act 1995 (NSW). Reports from two other anatomical experts questioned the validity of Professor H’s conclusions, arguing that his methods were too subjective given the circumstances.

Prior to the jury being empanelled, a voir dire was held to determine whether Professor H’s evidence was based (wholly or partially) on his 'specialised knowledge' (arising from his training, study or experience).

Professor H identified his specialised knowledge as anatomy, biological anthropology, and 'forensic identification' – which he described as the 'comparison of individuals based on the inspection of images'.  Since his specialised knowledge in the field was accepted, the relevant question was whether the evidence he presented was (at least partially) based on that specialised knowledge – and not merely a subjective opinion based on common-sense or ordinary judgement. 

At trial, Professor H's report was allowed into evidence, with Bozic DCJ determining on the voir dire that the expert’s opinions were based on his specialised knowledge. The defence appealed on this issue to the Court of Criminal Appeal, but Macfarlane AJ dismissed  the appeal on the basis that:

The prosecution submitted that the present case could be differentiated from Morgan, because Professor H's report in the latter case went one step further by concluding there was a 'high degree of anatomical similarity' between people in two images. 

In a unanimous judgement, French CJ and Keifel, Bell, Gageler and Keane JJ allowed the appeal, concluding that Professor H's opinion was not based wholly or substantially on his specialised knowledge:

“Professor H's opinion was not based on his undoubted knowledge of anatomy. Professor H's knowledge as an anatomist, that the human population includes individuals who have oval shaped heads and individuals who have round shaped heads (when viewed from above), did not form the basis of his conclusion that Offender One and the appellant each have oval shaped heads. That conclusion was based on Professor H's subjective impression of what he saw when he looked at the images.”

“… it would have been open to prosecuting counsel in the course of her closing address to have invited the jury to inspect the images and find that Offender One and the appellant share each of the characteristics identified by Professor H without the necessity of evidence.”

Aside from this guidance as to s 79(1) of the Evidence Act, the judgment also cautioned against using unnecessarily technical terms in expert reports:

“Professor H's evidence gave the unwarranted appearance of science to the prosecution case that the appellant and Offender One share a number of physical characteristics. Among other things, the use of technical terms to describe those characteristics – Offender One and the appellant are both ectomorphic – was apt to suggest the existence of more telling similarity than to observe that each appeared to be skinny.”

In this case, the wording used by the expert in his report was not only unhelpful, but had the potential to mislead the intended audience (the jury). This case and others⁵ demonstrate a willingness by the Australian courts to more closely scrutinise expert evidence, in terms of its admissibility, the way that it is presented, and its use at trial. 

Prior to this decision, some commentators had suggested⁶ that Australian courts were admitting too many novel forms of expert evidence. In the foreword to our recent book Expert Evidence: Recent Cases⁷, barristers Ian Freckelton QC and Hugh Selby discussed R v Dastagir,⁸ a similar case where expert CCTV identification was allowed by the Supreme Court of South Australia. They disagreed with that Court’s liberal approach to admissibility, arguing that unless it is specialised and enabling to the layperson, juries do not require ‘expert help’ on everyday matters such as the recognition of a face: ‘If there is something specialised about it then every cosmetic sales person who spends their days advising store customers what to apply to their face is equally expert help to jurors’.

As always, experts should be as clear as possible in explaining their methodology, ensuring that their opinions are expressed in clear and appropriate language and are confined to their area of expertise – or the courts may not accept their opinions at ‘face value’.