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Supreme Court 13 August 2015

R v Xie (No 19)

[2015] NSWSC 2130

Homicide
CRIMINAL LAW ADMISSIBILITY DNA EVIDENCE ADDENDUM TO R V XIE (NO 18)

Citation: R v Xie (No 19) [2015] NSWSC 2130
Court: Supreme Court of New South Wales
Date: 13 August 2015
Judge(s): Fullerton J

Background

This decision is an addendum to an earlier ruling in R v Xie (No 18) [2015] NSWSC 2129, in which Fullerton J had already ruled on the admissibility of DNA evidence in a criminal trial involving multiple alleged homicides. The accused was charged in connection with deaths at a residential property, and DNA analysis formed a significant part of the Crown's forensic case.

The Crown sought to lead further evidence from its DNA expert, Mr Goetz, concerning the similarity between a mixed-contributor DNA profile found at the crime scene (Item 616) and a profile obtained from a sample taken from the garage floor of the accused's home (Item 550). The Crown's case theory was that the similarity supported an inference that blood from the deceased had been transferred from the crime scene to the garage.

Following the earlier ruling, a dispute arose about the precise scope of questions the Crown proposed to put to Mr Goetz when his evidence in chief resumed before the jury. A voir dire (a hearing conducted in the absence of the jury to test admissibility) was held to determine whether the proposed further evidence could be admitted without breaching the existing ruling.

  • Whether the further evidence the Crown proposed to elicit from Mr Goetz was covered by the earlier ruling in R v Xie (No 18)
  • Whether Mr Goetz's proposed evidence about the proportional similarity of allele peak heights between Items 550 and 616 satisfied the requirements for expert opinion evidence under s 79 of the Evidence Act 1995 (NSW)
  • Whether admitting that evidence would create a real risk of unfair prejudice to the accused that jury directions could not adequately address

Decision

On the voir dire, Mr Goetz explained that in his ordinary casework, analysts do not routinely compare mixed-contributor DNA samples for similarity. They review such samples only to determine whether a single-source profile can be extracted for database upload. His practical experience with mixed-contributor profiles was therefore general rather than the product of systematic comparative analysis.

Fullerton J found that the proposed questions about multiple crime scene samples were inadmissible on their face. Mr Goetz had in fact focused only on Item 616 in his comparison with Item 550, not on a range of crime scene samples as the Crown's questions implied. The Crown acknowledged this.

The more difficult question concerned whether Mr Goetz could give evidence about the proportional similarity of allele peak heights between Items 616 and 550 as an objective feature of the profiles, without venturing an opinion about the degree or significance of that similarity. Fullerton J concluded that this distinction could not be maintained in practice. Any evidence of a similarity in proportions necessarily risked inviting a qualitative assessment of how similar, and Mr Goetz had himself repeatedly acknowledged he could not quantify or describe that degree of similarity scientifically. Requiring the defence to cross-examine within those constraints would impose an unfair forensic burden.

Fullerton J held that, although the additional feature of similarity had probative value, it was not in the same category as purely objective features such as allele numbers. The danger of unfair prejudice, particularly the risk that a lay jury could not distinguish a qualitative observation of similarity from a conclusion that the profiles were for all practical purposes identical, outweighed that probative value. The further evidence was disallowed.

Orders Made

No orders were made in this decision.

Key Takeaways

  • Expert opinion evidence under s 79 of the Evidence Act 1995 (NSW) requires the witness to have relevant training, study, or experience sufficient to support the specific opinion sought, not merely general familiarity with a related field.
  • Where a DNA analyst has not undertaken systematic casework analysis to support a comparative opinion, evidence framed as an "objective" observation may still fall short of the admissibility threshold if it implicitly depends on qualitative reasoning the expert cannot scientifically substantiate.
  • A distinction between stating the fact of similarity and commenting on the degree of similarity may be too fine, in practice, to be maintained in evidence before a jury, particularly where cross-examination cannot test the opinion without itself introducing impermissible reasoning.
  • Probative value alone does not secure admission; Fullerton J found that the risk of a lay jury treating a highly technical similarity observation as effectively establishing identity between DNA profiles created an unfair prejudice that directions could not cure.
  • The decision illustrates how pre-trial rulings on expert evidence continue to shape the permissible scope of questions put to witnesses when evidence in chief resumes, with the voir dire process available to test whether proposed questions stray beyond those limits.

Legislation and Cases Referenced

Legislation:
- Evidence Act 1995 (NSW), s 79 (opinion evidence exception for persons with specialised knowledge)

Cases:
- R v Xie (No 18) [2015] NSWSC 2129