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Sexual assault defence – DNA expert role

Helen Roebuck has extensively proffered DNA expert witness testimony throughout Australia and select international jurisdiction in matters of sexual assault, murder, manslaughter, explosives, firearms, and class A drugs.

A DNA expert provides explanation and interpretation of the DNA testing and results to the court and jury in a clear and straight forward manner.

The expert does not favour either party nor seek to determine if one version of events is true or false.

When reviewing DNA regarding a sexual assault defence, we are typically working in consideration of the prosecution and defence version of events.

As a forensic biologist expert witness, our participation within a sexual assault defence may be limited to the technical issues at hand in a broad advisory capacity, or with a detailed review and production of a written DNA expert report.  

We regularly provide brief initial interpretation and advice, and also often work intensively on matters as they progress through each stage of the justice system including oral testimony at hearing.

A DNA expert witness functions alongside and under instruction of a criminal defence lawyer and or barrister.

Sexual assault defence – DNA expert opinion

Our expert opinion within a sexual assault defence centres around the scientific and forensic consideration of the biological evidence. The biological evidence assessment may include reviewing the DNA profiles and biological fluids sample interpretation conducted by the prosecution laboratory. The review process may also evaluate a range of carefully conceived scenarios and the resultant likelihood of the biological evidence (including DNA and body fluids) in connection with those scenarios.

 A few examples of the scenarios we may give consideration to ;

• * Could the defendants’ DNA have been located on the complainants’ jeans as a result of the two people brushing against each other at the pub?
• * If brushing against each other put the defendants DNA on the complainants’ jeans, could the complainant have moved the defendants DNA into her own underpants when later using the toilet?
• * Was the semen deposited by the defendant, or could it have been deposited by another person?

This matter in detail

Prosecution  Version

In this specific matter, it was alleged that the complainant and the accused were socialising amongst a group of people at a licenced venue. After a number of hours, the accused and defendant left the venue, at which time the defendant offered to drive the complainant home. During the drive to the complainant’s home, the accused made multiple intimate advances upon the complainant, which were rejected. Upon reaching the complainants dwelling, the accused entered the home under the pretext that he needed to use the bathroom. Soon after entering the dwelling, the defendant did force himself upon the complaint which included vaginal penetration of both the penis and digits.

Defence Version

The defendant’s version set out that the parties were socialising together at a hotel and that the complainant was driven home. It was further stated that there was reciprocal external contact in the vehicle during the drive to the complainants dwelling. Upon arrival, the complainant invited the defendant inside. The defendant asserted that there was external contact and kissing of a reciprocal nature. During this process, the defendant proceeded to commence undoing the complainant’s jeans. This effort from the accused was met with the complainant saying that she didn’t want to have sex. The defendant claimed that he left the premises shortly thereafter and did not penetrate the accused in any way.

Video footage

CCTV footage form the venue confirmed that the parties were speaking at different time points as they and the other patrons moved around the venue, visiting the bar, toilets, poker machines etc and returned to their seats at the bar and other tables. Variously, the footage shows that the accused and the complainant, along with the other persons within the group would occupy different chairs and locations, touching various surfaces, glasses and tables etc. On multiple occasions the complainant can be seen casually touching or coming into contact physically with the defendant and vice versa.

DNA evidence

The crown laboratory analysed samples from the complainant’s shirt, jeans and underwear. A SAIK (medical examination) was conducted, and various clothing and vaginal samples were analysed. There was a mixed DNA profile which identified the defendant, the complainant, and an unknown male individual.

Sperm cells were identified. Our detailed analysis revealed that the sperm cells detected could not be scientifically linked the defendant.

DNA is highly transient

DNA is highly transient and can be readily deposited, picked up and then re deposited over and over. Within an everyday environment like a hotel, there will be many peoples DNA on any number of surfaces. One persons’ DNA can be deposited by touching a table for example, and then be redistributed throughout the environment and onto other people from one person to another, to another and so on.

Biological fluid evidence

Presumptive testing was conducted which identified sperm cells (semen). The mere presence of semen may not, and in this case could not be taken to mean that the defendant had deposited the semen.

DNA in the justice system

In this sexual assault defence matter, we were instructed by defence soon after charges were laid. The DNA evidence identified the defendant at a likelihood ratio of 100 billion.

Various sets of documentary evidence are produced by the crown relating to the DNA and biological fluid evidence. In reviewing this matter, we recommended the subpoena of further evidence of the government laboratory.

During the review process, we formed the view that the mixed DNA profile could not in fact be scientifically attributed to the sperm cells. The significance is that whilst the semen could have been deposited by the accused as alleged, it could alternatively have been deposited by a different person. The science could not weight either scenario as more or less likely.

100 billion times more likely

The DNA samples reviewed did match the defendant’s reference sample, and the statistical likelihood ratio of 100 billion was appropriate. However, we did consider that the DNA could have been deposited to the complainants clothing and person through general contact at the hotel, vehicle and home environment. Once the defendants DNA was located upon the complainants clothing and person, it may have been transferred to the various places as sampled by way of everyday actions, which may have included toileting. Further, science could not contribute anything as to which scenario is more or less likely than the other.

Voir Dire Hearing

Certain DNA evidence is considered more prejudicial than it is probative by the courts in accordance with Section 137 of the evidence Act.

When the court makes this finding, admittance of the evidence must be refused.

This hearing process is referred to as Voir Dire.

“ EVIDENCE ACT 1995 – SECT 137;

Exclusion of prejudicial evidence in criminal proceedings

137 Exclusion of prejudicial evidence in criminal proceedings

In a criminal proceeding, the court must refuse to admit evidence adduced by the prosecutor if its probative value is outweighed by the danger of unfair prejudice to the defendant.”

Roebuck Forensics is extensively experienced in the proffering of DNA expert evidence to be served and heard at Voir Dire hearing.

One such published NSW Voir Dire hearing where the court ruled with consideration to Helen Roebuck’ opinion regarding DNA transfer is R v KE [2019] NSWDC 349 (16 July 2019)

Ruling – Judge Grant

“ [16] It is her [Helen Roebuck] 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.

[41] In DPP v Wise the Court made this observation at [70]:
“Moreover, one of the dangers associated with DNA evidence is what has become known as the ‘CSI effect’. The ‘CSI effect’ is a reference to the atmosphere of scientific confidence evoked in the imagination of the average juror by the descriptions of DNA findings. As we have explained, as a matter of pure logic, the DNA evidence has little or no probative value. By virtue of its scientific pedigree however, a jury will likely regard it as being cloaked in an unwarranted mantle of legitimacy — no matter the direction of a trial judge — and give it weight that it simply does not deserve. The danger of unfair prejudice is thus marked, and any legitimate probative value is, at best, small.”

[42] Having regard to the ‘CSI effect’ the jury would be tempted to place undue weight on the evidence which has almost no probative value.

[43] I refuse to admit the evidence sought to be adduced by the prosecution because if it does have probative value, which I very much doubt, that value is outweighed by the danger of unfair prejudice to the accused by reason of the possibility of misuse of the evidence by the jury.”

After DNA evidence is excluded

The trajectory of a criminal prosecution following the exclusion of DNA evidence, will be contingent upon numerous factors, however it is reasonable to say that sexual assault matters regularly rely with significance on the DNA evidence.

In this particular matter, once the DNA evidence was excluded, the charges were withdrawn by the ODPP.

Can DNA alone be used to prove sexual assault?

In theory, DNA evidence should not be singularly relied upon, however DNA evidence is regularly a significant evidentiary factor.

DNA expert and Legal Aid funding

The matter in this case study was legal aid funded. We regularly conduct matters which are fully funded by NSW Legal Aid.

DNA expert cost

The hourly cost of our service is comparable to that of a skilled and experienced criminal lawyer.

DNA expert preliminary review

We can conduct a preliminary review of the DNA evidence in your matter. This would generally cost approximately 2 to 4 hours of our time.

How to engage Roebuck Forensics as your DNA expert

The defence of sexual assault charges is a serious undertaking, with irreversible consequences. We recommend that you engage a highly skilled defence lawyer who will engage us directly and be able to discuss your specific matter with us.

We can assist directly with information that you will be able to discuss further with your solicitor.