DNA evidence can be ruled inadmissible in Australian sexual assault cases.
It is often assumed that DNA evidence will automatically be heard at trial. In reality, courts can exclude DNA evidence before a jury ever sees it
When DNA Evidence Is Excluded Before Trial – R v Ke 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 prosecution allegation
- It was alleged that Mr Smith sexually assaulted his partners teenage daughter.
- This was said to occur in his bed.
- The DNA profile from Mr Smith’s bedsheet was relied upon as proof.
2. The defence position
Mr Smith said this never happened but acknowledged being in a sexual relationship with the complainant’s mother.
3. What a DNA report actually means
DNA reports can be problematic because they merely list certain DNA results.
Important note: there is almost always other DNA work conducted by the lab which is not contained in the expert report. The DNA casefile must be reviewed if you wish to understand what the unreported and reported results can support.
The expert report in this matter failed to consider the actual circumstances of Mr Smith and his partner.
The report stated these specific words:
“The DNA profile is 1 billion times more likely to be obtained if the complainant is a contributor.”
4. Why DNA statistics and likelihood ratios can be wrong
Mr Smith and his partner have shared the bed.
The complainant was the biological daughter of Mr Smith’s partner.
Because of this, the DNA in fact might be from the complainant’s mother.
The DNA report failed to evidence the appropriate mother comparison.
5. How STRmix and DNA likelihood ratios are calculated
Computer modelling software compared the genetic markers on the complainants DNA profile to the sample from the bedsheet.
The software, known as STRmix did not make a mistake, rather the analyst failed to report the complainants mother as a possible DNA contributor to the sample.
6. How DNA evidence can be wrong
- Errors cannot be established on the face of the expert report.
- We conducted a scientific review of the DNA casefile including the STRmix extended outputs.
- We established that the mother was more likely the source of the DNA, than the complainant.
- The prosecution withdrew the evidence following receipt of our report.
7. When DNA evidence can be misinterpreted in criminal cases
Many criminal allegations are conceived in situations where people and their relatives are intertwined. These matter specific factors should be carefully evaluated against any DNA results.
Care is advised when:
- Relatives co habit and visit
- Close social contact exists
- People share bedding or clothing
- Worn clothing and bedding is stored and laundered together
When DNA evidence looks conclusive but isn’t
- If you deny the allegation but the DNA report seems conclusive, this may be a red flag.
Do you need a DNA expert?
A criminal lawyer and a DNA expert are two very different specialities.
DNA evidence seems simple within the expert report but is highly complex beneath the surface.
One cannot truly determine the accuracy of the expert report or what it actually means without digging a little deeper scientifically.
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
In many matters, a short scientific review of the DNA casefile is enough to determine whether the DNA work conducted by the lab genuinely supports the allegation or whether the DNA results support an alternate explanation of events.
