Sexual Assault 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.
WHEN COURTS EXCLUDE DNA EVIDENCE BEFORE TRIAL: SEXUAL ASSAULT CASE EXPLAINED
DNA evidence is often treated as final.
You might assume that DNA evidence will automatically be heard at trial.
The jury does not necessarily have to hear the DNA evidence in all matters.
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.
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 non-sexual social contact?
- Might the jury understand the results to be more definitive than they actually were?
3. The pre-trial DNA hearing…CAN DNA EVIDENCE BE EXCLUDED?
- The pre-trial hearing saw an application to challenge DNA evidence admissibility.
- This is legally described as – whether the probative value of the evidence is outweighed by the risk of unfair prejudice.
- This occurred during a pre-trial hearing (known as a voir dire), where the two parts of the law and science were put before the judge.
- The DNA evidence in court was ventilated by prosecution and defence scientific experts, who were both questioned and cross examined.
- The lawyers made legal submissions.
- The judge heard the evidence and refused the DNA.
4. Why the DNA evidence was refused
- 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 one part legal and one 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.”
Helen Roebuck’s expert opinions were formulated through a detailed scientific review of:
- Contemporaneous records
- Electropherograms
- DNA statistics
- STRmix extended outputs
- The labs internal laboratory validation records
- Published scientific research data
5. 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.
- Suitability of a given matter lies predominantly with the science and specific allegation.
Do you need a DNA expert?
Legal defence and DNA interpretation are two distinct fields of expertise.
An exclude DNA evidence application involves complex legal process.
It also requires refined scientific review and interpretation.
The courts approach to exclusion applications continually evolve as scientific advancements make their way into the courtroom.
Helen Roebuck frequently works matters which result in DNA exclusion.
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.
