DNA evidence can be ruled inadmissible in Australian courts. It is often assumed that DNA evidence will automatically be heard at trial. In reality, courts can exclude DNA evidence before a jury ever hears it.
This is known as DNA evidence exclusion. It occurs when a judge determines that the jury should not hear the DNA evidence at all.
DNA Evidence Exclusion in Criminal Cases
DNA evidence exclusion does not mean testing was not conducted.
It means the court has decided that the way the DNA evidence would be presented could mislead the jury, or that its probative value is outweighed by the risk of unfair prejudice.
In Australian criminal courts, this decision is made before trial during a separate hearing. The judge considers both the scientific reliability of the evidence and the legal rules governing admissibility.
When DNA evidence is excluded, the jury never hears it.
When Courts Exclude DNA Evidence Before Trial: Sexual Assault Case Explained
DNA evidence is often treated as final.
You might assume that once DNA is detected, the jury must hear it.
That is not correct.
The jury does not necessarily have to hear the DNA evidence in all matters.
Courts have the power to exclude DNA evidence where it risks being misunderstood or overstated.
This case explainer of R v Ke [2019] NSWDC 349 sets out why the DNA evidence was excluded before trial.
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.
Judge Grant stated:
“ On this application the defence have tendered a report of Mrs Helen Roebuck. It was her opinion that because the DNA profile cannot be attributed to a specific biological material it is a trace DNA.
I was informed that a saliva test was not conducted.
It is her opinion trace DNA can be transferred directly and indirectly. It is not possible to determine whether the DNA was deposited through direct contact with the vulval area, or whether DNA was deposited on to another surface and then transferred to the vulva…when individuals are in social contact or reside in the same property there is an increased opportunity of secondary and subsequent transfer of DNA.
She told me that the amount of DNA extracted from the vulval swab was a low amount; it was a couple of hundred cells detected, but not a large amount. She agreed that people can shed up to 30,000 cells per day.”
5. How DNA Evidence Can Be Challenged in Court
DNA evidence in court is typically challenged through detailed scientific review of the laboratory casefile and the assumptions underlying the reported results.
Helen Roebuck’s expert opinions in this matter were formulated through review of:
- 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
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
Helen Roebuck is a strongly credentialed and highly regarded forensic DNA expert, trusted within both the legal and scientific communities. She is the most prolific and judgment-published independent DNA expert witness in Australia
Having reviewed DNA evidence in thousands of indictable matters over the last 25 years including homicide, sexual assault and drugs importation.
Accepting simple and complex Legal Aid and privately funded briefs across Australia, New Zealand and select international jurisdictions.
Published judgments:
WA v Piccioni [2025] – WA District Court
R v Murphy [2024] – NSW District Court
LGBTIQ Hate Crimes Inquiry [2023] – NSW
R v Granaghan [2022] – N Ireland Crown
R v Perre [2021] – SA Supreme Court
R v Ke [2019] – NSW District Court
R v TAL [2019] – QLD Supreme Court
R v Haouchar [2025] – NSW District Court
R v Ahmad [2024] – NSW District Court
Evans v R [2023] – NSW Supreme Court
R v Tsakirios [2021] – NSW District
R v Kabbout [2020] – NSW District Court
A short forensic review can often determine whether the DNA evidence genuinely supports the allegation and whether the matter has scientific merit to support an application for exclusion of the DNA.
