DNA Evidence Exclusion in Criminal Cases

When Courts Exclude DNA Evidence Before Trial: Sexual Assault Case Explained

2025: DNA contamination firearms – Exclusion ending proceedings ⟶

1. The sexual assault allegation

It was alleged that oral sex upon a female occurred.
DNA testing was carried out by the government laboratory.
The scientific results were relied upon as support for the prosecution.
At first glance, the presence of DNA appeared significant.
But presence alone does not determine whether the evidence is admissible.

2. What the DNA report did and didn’t say

The government DNA lab reported the accused’s DNA on the complainants genitals.
The report could not conclusively link the DNA to a specific body fluid.
Might the DNA be from oral sex?
Or might DNA transfer have occurred during non-sexual social contact?
Might the jury understand the results to be more definitive than they actually were?
These questions became central to whether the DNA evidence should be heard at all.

3. The pre-trial DNA hearing…CAN DNA EVIDENCE BE EXCLUDED?

Before trial, the defence made an application challenging the admissibility of the DNA evidence.
In criminal trials, DNA evidence is a form of forensic scientific evidence, and like any forensic evidence it may be challenged or excluded where its probative value is outweighed by the risk of unfair prejudice.
This occurred during a pre-trial hearing (known as a voir dire), where both the legal issues and the scientific issues were put before the judge.
The DNA evidence was examined in detail.
Both prosecution and defence scientific experts were questioned and cross-examined.
The lawyers made legal submissions.
The judge then ruled that the DNA evidence should not be admitted.
The jury would never hear it.

4. Why the DNA evidence was excluded

The problem in this case was not whether DNA was detected.
The question was whether the jury should ever hear this specific DNA evidence.
That question is part legal and part scientific.

5. How DNA Evidence Can Be Challenged in Court

Contemporaneous records
Electropherograms
DNA statistics
STRmix extended outputs
The labs internal laboratory validation records
Published scientific research data on secondary DNA transfer
It was that detailed forensic review which led to the exclusion of the DNA evidence

1 billion DNA statistic – challenged – withdrawn →

6. How DNA exclusion applies to your matter

An application to exclude DNA evidence can be made in all states of Australia.
One matter lends itself to exclusion more so than another.
Challenging DNA evidence depends on the science and the specific allegation.
Legal defence and DNA interpretation are two distinct fields of expertise.
An application for DNA evidence exclusion involves complex legal process.
It also requires careful DNA expert review.
The courts’ approach to exclusion applications continues to evolve as scientific understanding develops.
In some matters, the correct forensic analysis does not simply weaken the evidence — it prevents the jury from hearing it at all.
Helen Roebuck frequently works on matters where DNA evidence is excluded before trial

welcome

Helen Roebuck DNA expert giving evidence

‘I engaged Helen Roebuck to independently examine a complicated DNA issue arising from a Rape matter. Ultimately, the jury returned a verdict of ‘Not Guilty’ on all counts. We couldn’t have done it without Helen.’

Jasmine Pisasale Director, Slade & Parsons

‘a complicated DNA contamination matter. Although the DNA evidence initially seemed damning to the accused, the client was acquitted of all charges. Helen’s advice and evidence at Trial was invaluable.’

Kestin Mildenhall Crockett Chambers

‘Helen was engaged on short notice. District Court of NSW trial we were faced with a “word on word” situation for a number of alleged sexual assaults, with very little independent evidence to assist the defence. The result was that the DNA evidence was not led, enabling the matter to be much shorter than would have been the case, which proceeded to “not guilty” verdicts on all counts.

John Gooley Stacks Collins Thompson

‘Her professionalism, dedication and expert knowledge were instrumental in the presentation of the defence case’.

Gabriel Chipkin Barrister

‘Very professional, organised, and most importantly a very impressive witness. I would not hesitate to refer her for any DNA related matters’.

Jane Murray Solicitor

‘Her evidence in Court was instrumental in establishing the deficiencies in the Crown’s DNA case, and in obtaining a great outcome for our client’.

Simon Kenny Barrister

‘Her work in unpicking and explaining the intricacies of STRmix including who was and was not a contributor to a complex DNA profile was amazing’.

Gilbert Aitken Barrister

‘Helen’s comprehensive report resulted in the prosecution determining not to adduce the DNA evidence’.

Andrew Culshaw Barrister

‘Helen’s report was the ” final piece of the puzzle ” and without it we would not have been able to prove our case’.

Michael Lee Lawyer

‘The first person I called was Helen to thank her for preparing me for a successful cross-examination’.

Maeve Curry Barrister

‘Opinion was detailed, concise and persuasive. I highly recommend Helen Roebuck’.

Amelia Ramsey Lawyer

‘I’d absolutely recommend seeking her guidance and opinion’

James Leaver Samuel Griffith Chambers

Helen Roebuck CV

Challenging DNA Evidence: When Courts Exclude It Before Trial