The State of Western Australia v Piccioni - [2025] WADC 69

JURISDICTION : DISTRICT COURT OF WESTERN AUSTRALIA
IN CRIMINAL

LOCATION:   PERTH
CITATION:   THE STATE OF WESTERN AUSTRALIA -v- PICCIONI [2025] WADC 69
CORAM:   ASTILL DCJ
HEARD:   18 SEPTEMBER 2025
DELIVERED          :   3 OCTOBER 2025
FILE NO/S:   IND 673 of 2021
BETWEEN:   THE STATE OF WESTERN AUSTRALIA

AND
TOMMASO NICOLA PICCIONI

Catchwords:

Criminal law - Evidence - Admissibility of DNA evidence - Where investigator mediated contamination occurred during execution of search warrant - Whether a jury would be able to make a reliable assessment as to direct transfer of DNA - Competing inferences of direct and indirect transfer - Whether evidence is relevant - Whether prejudicial effect of evidence exceeds probative value - Whether prejudicial effect causes unfairness

Legislation:

Criminal Procedure Act 2004 (WA)

Result:

Evidence inadmissible

Representation:

Counsel:

The State of Western Australia	:	Mr S M Stocks
Accused	:	Mr M A Perrella

Solicitors:

The State of Western Australia	:	State Director of Public Prosecutions
Accused	:	Perrella Legal

Case(s) referred to in decision(s):

Chamberlain v The Queen [No 2] (1984) 153 CLR 521
Creusot v The State of Western Australia [2022] WASCA 117
Edwards v The Queen [1993] HCA 63; (1993) 178 CLR 193
Festa v The Queen [2001] HCA 72; (2001) 208 CLR 593
Goldsmith v Sandilands [2002] HCA 31; (2002) 76 ALJR 1024
HML v The Queen [2008] HCA 16; (2008) 235 CLR 334
Mukevski v The State of Western Australia [2010] WASCA 138
Pennington v The State of Western Australia [2013] WASCA 98
R v Baden-Clay [2016] HCA 35; (2016) 258 CLR 308
R v Hillier [2007] HCA 13; (2007) 228 CLR 618
Roach v The Queen [2011] HCA 12; (2011) 242 CLR 610
Shepherd v The Queen (1990) 170 CLR 573
Smith v The Queen [2001] HCA 50; (2001) 206 CLR 650
Zoneff v The Queen [2000] HCA 28; (2000) 200 CLR 234

ASTILL DCJ:

Background

By way of application dated 8 August 2025 (the application), the accused applies pursuant to s 98 of the Criminal Procedure Act 2004 (WA) (the Act) for directions excluding the admissibility of 'DNA evidence sought to be adduced by the prosecution' in the trial of the seven charges presented against him by way of indictment dated 1 August 2024 (indictment).
The indictment charges the accused with four counts of possessing firearms and three counts of possessing ammunition, located by police at a storage container on 21 August 2019 and is listed to commence trial on 13 October 2025. He was first charged on 14 October 2019. It is unnecessary for me to undertake a detailed analysis of the causes of the delay other than to note the history of these proceedings has been unfortunate and protracted. It is the delay itself and the effect it has upon the reliability of human memory which is relevant to the resolution of this application. This is a matter that I will return to below.
The 'DNA evidence' sought to be excluded is the PathWest testing of swab F0915160-0 which provided a mixed profile assumed to have come from four contributors. From that mixed profile, a profile consistent with the accused's DNA reference sample was identified. The statistical weighting attributed to that analysis was calculated to be more than 100 billion to one. The mixed DNA profile was not suitable for further interpretation.
The accused was originally jointly charged with his co-accused, Darcy Doyle. On 13 February 2024, just prior to the matter proceeding to trial, Gething DCJ (as his Honour then was) severed the indictment. The State proceeded to trial against Mr Doyle in relation to associated charges that related to Mr Doyle alone.
On 1 August 2024 the State discontinued five of the seven charges that Mr Doyle had been jointly charged with the accused. By way of discontinuance dated 17 September 2025, the State discontinued the remaining two charges against Mr Doyle. Consequently, in relation to the seven charges the subject of the indictment, the State now proceeds solely against the accused. It is notable that no forensic evidence was obtained from DNA testing of the exhibits which connected Mr Doyle to any of the firearms or ammunition with which he was jointly charged with the accused. This perhaps gives some preliminary indication as to the significance of the DNA evidence to the prosecution case against the accused.
The application is founded on the basis that the prejudicial effect of admitting this evidence outweighs any probative value it might possess, owing to what is described as 'mass contamination' during the search and seizure of the exhibits later submitted for forensic testing. While the prosecution concedes that deficiencies in the conduct of the search may have impacted the forensic integrity of the seized material, it maintains that these shortcomings do not amount to 'mass contamination', and instead should be regarded as, at most, 'incompetence'.
To be able to make a proper assessment of the strength of the DNA evidence, it is necessary to examine the significance it holds in the prosecution case.

Overview of prosecution case

On 21 August 2019, West Australian police (WAPOL) officers executed a search warrant at 100 Cutler Road in Jandakot. This is the location of a storage facility known as 'Billabong Self Storage'. Their area of interest was storage unit 8.
The search was audiovisually recorded and conducted in the presence of Mr Doyle. At that stage, the accused was not a suspect and was therefore not present. Although the execution of the search was recorded, consistent with what is often referred to as 'standard practice', the recording did not capture the entirety of the search.
The recording commenced at 4.58 pm when officers arrived at the scene. Upon arrival the unit was locked. At 5.04 pm, the camera was switched off whilst officers endeavoured to gain entry. It was turned back on very shortly thereafter when officers managed to successfully unlock the unit.
At 5.04 pm 'and a bit' a camera pan of the unit was conducted which showed it contained various items and belongings. The contents could broadly be described as including a collection of car parts, multiple storage tubs containing various parts and equipment, and items that were covered by blankets and sheets. The recording was again suspended at 5.05 pm after the pan was completed.
At 5.15 pm the recording was switched back on. The officer in charge of the search advised the search had been stopped 'a couple of minutes ago' as officers had located what they believed to be firearms during the search. Four of the firearms that were found are the subject of counts 1 ‑ 4 on the indictment.
It is clear from the recording that when it was switched back on the firearms were no longer 'in situ' and had been moved, along with the remaining contents of the unit. Some of the firearms were within cases or containers that evidently had already been opened by the time the recording commenced at 5.15 pm. Given the search had been stopped 'a couple of minutes' prior to the recording resuming, the search of the entire storage unit and the removal of its contents had been conducted in less than 10 minutes.
Count 1 relates to one of two rifles located within a black firearms case. The count particularises a repeating rifle as being the subject of the charge. The accused was also, at one stage, charged with being in possession of the second rifle, being a Francotte single shot rifle. However, on 22 November 2022 that charge was discontinued. What can be seen on the recording is the case had already been opened, as well as a gun bag in which one of the rifles was located.
Count 2 particularises the firearm the subject of this charge as being a Zoraki 9 mm pistol. This firearm was located within a grey/green cooler bag which had been removed from the storage unit and placed on the bitumen road out front. When examined, it was picked up and placed on the bare concrete of the storage unit. Inside the bag were two other pistols, a revolver which was incapable of firing and an imitation pistol, neither of which the accused has been charged with. After going through these items, the recording was paused at 5.43 pm to 'allow the exhibits officer to catch up' as they were concerned about maintaining the forensic integrity of the items seized.
The recording resumed nine minutes later at 5.52 pm. By that time, a black case had been placed on the bare concrete floor of the storage container. It was clear the case was not originally in situ, as it now occupied the same spot where the firearms case containing the two rifles had earlier been positioned. The first firearm retrieved was a Smith & Wesson Magnum revolver, the subject of count 3 and the focus of the disputed DNA evidence. The revolver is visible inside the case, lying loosely beneath a flap of fabric that required lifting to access it. After examining and handling the firearm, the officer is observed changing into a new pair of gloves.
Secreted under a second flap was a second pistol which is the subject of count 4. At the time of removing the pistol from the case, the pistol was loaded. The recording unexpectedly finishes whilst the officer is still holding this firearm.
Counts 5 ‑ 7 concern ammunition of various calibres seized from different locations within the storage unit. Each count represents the total quantity of ammunition of a particular calibre, rather than its specific location. For the purposes of this application, these counts carry little relevance. A partial pistol was also found within a blue lunch bag along with a black fabric glove. The accused was not charged with this partial pistol. None of the firearms the subject of counts 1 ‑ 4 were located inside this lunch bag and it has little relevance to the determination of the application other than to note similar handling difficulties were observed when dealing with this exhibit.
Throughout the recording, it is the same officer who can be seen handling and dealing with each of the firearms and ammunition the subject of the seven counts. In the various materials received (discussed in further detail below) this person, who is not identified, is referred to as the 'primary examination officer' (PEO). To maintain consistency in terminology, I will adopt this phrase when referring to this person.

Circumstantial case

The State's case regarding possession in relation to all seven counts is a circumstantial one. The proposed DNA evidence forms a significant part of it.
In the State's written submissions dated 15 September 2025 (State's submissions), the State submits the DNA evidence 'complements an existing circumstantial case, and is not an indispensable link in the chain of reasoning'.[1] As can be seen, the State suggests that the DNA evidence operates as part of the circumstantial case as a 'strand in the rope' in the way described in Chamberlain v The Queen [No 2],[2] as opposed to a 'link in the chain' being a reference to the indispensable intermediate fact reasoning discussed in Shepherd v The Queen.[3] That circumstantial case was outlined as part of further correspondence provided to the court on 17 September 2025.[4]
[1] State's submissions, par 4.
[2] Chamberlain v The Queen [No 2] (1984) 153 CLR 521, 535.
[3] Shepherd v The Queen (1990) 170 CLR 573, 579.
[4] See email from DPP dated 17 September 2025 at 11.24 am.
A significant component of the prosecution's circumstantial case is directed towards establishing the accused's connection and access to unit 8. For the purposes of determining the application, it was not disputed that this inference was available and capable of being drawn from those collection of facts. This is of course relevant towards establishing the accused's access to, and ability to exercise control over, one or more of the firearms the subject of the indictment.
However, during oral submissions, the State quite properly acknowledged that the evidence available as part of its circumstantial case to establish knowledge and an intention to exercise control was much more limited.[5] To establish this aspect of the accused's possession, the State primarily relied upon:
(a)the proposed DNA evidence;
(b)a lie, or lies, which the State contends was told by the accused out of a consciousness of guilt (commonly referred to as 'an Edwards[6] lie'); and
(c)what the State suggests is post‑offence conduct by the accused 'clearing out' unit 8 on 1 September 2019 following him becoming aware of the police search on 21 August 2019.
[5] ts 604.
[6] Edwards v The Queen [1993] HCA 63; (1993) 178 CLR 193.
The lie, or lies, contended by the State as amounting to an Edwards lie were not specifically identified in any degree of detail when hearing the application. The State submitted, broadly, that the accused 'tells Edwards lies when police ask him questions about unit no.8 on 19 September 2019' and that 'the only reasonable inference for telling the lies is that [the accused] lied to distance himself from unit no.8 because he well knew admitting he was accessing the unit would implicate him in these offences'.[7]
[7] See email from DPP dated 17 September 2025 at 11.24 am.
The defence submit what is characterised as being 'an Edwards lie' is rather 'a Zoneff[8] lie',[9] that is, a lie going towards the accused's credibility only and not capable of permitting an inference of guilt being drawn against the accused. The defence were unable to respond in any detail to the alleged post‑offence conduct as it had not been made clear prior to the directions hearing that the State would rely upon this conduct in this way. However, by way of correspondence sent to the court after the directions hearing had concluded, the defence contended:[10]
… the weight of the available evidence cannot reasonably support the State's suggestion that the alleged 'post offence' conduct can be used in reasoning towards guilt, and it ought to be excluded from his Honour's determination, so far as it might have been relevant, on the admissibility of the DNA evidence.
[8] Zoneff v The Queen [2000] HCA 28; (2000) 200 CLR 234.
[9] ts 606.
[10] See email from defence counsel dated 19 September 2025 at 11.50 am.
The defence submit that when the evidence characterised by the State as being 'post‑offence conduct' is considered in its proper context, at its highest what it is capable of showing is the accused attending and 'cleaning out' the unit after being requested to do so by the operators of Billabong Self Storage due to the lease being unilaterally terminated.
An accused person's post‑offence incriminating conduct, including lies, is circumstantial evidence that a jury can accept and act upon if the conduct constitutes an implied admission against interest. A jury is not required to be satisfied beyond reasonable doubt that the post‑offence conduct establishes guilt. That is, a jury need not be satisfied there is no other explanation of the post‑offence conduct reasonably open on the facts, unless the post‑offence conduct is an indispensable link in the chain of reasoning on which proof of guilt depends.[11]
[11] Creusot v The State of Western Australia [2022] WASCA 117 [57].
For the purposes of determining the application, I must consider the inferences that are available collectively from the evidence available to the State.[12] Ordinarily, where competing inferences are available, the assessment of the plausibility and resolution of those competing inferences is a question for the jury rather than as part of the resolution of a preliminary question as to admissibility.[13] Nevertheless, it will be necessary for a trial judge to be satisfied conduct is capable of establishing an inference as to consciousness of guilt before it can be left to a jury to use in that fashion.[14]
[12] R v Hillier [2007] HCA 13; (2007) 228 CLR 618, 637 ‑ 638.
[13] R v Baden-Clay [2016] HCA 35; (2016) 258 CLR 308, 324 (Baden-Clay).
[14] Pennington v The State of Western Australia [2013] WASCA 98 [104].
Without deciding whether the conduct of 'cleaning out the unit' alleged by the State is capable of constituting 'post‑offence conduct', I am prepared to accede to the defence request that it be disregarded for the purposes of this application. In my view, consideration of the alleged post‑offence conduct does not materially strengthen any inference that the accused knew of, or intended to exercise control over, the firearms found in the unit, beyond what is already potentially established by the alleged Edwards lie.
As for the defence submission that what the prosecution submits is an Edwards lie is in fact a Zoneff lie, ultimately that will be a question for the trial judge to determine. For the purposes of assessing the current application, I proceed on the basis that it is capable of being used as an Edwards lie (without determining that it is) and consider the significance of the DNA evidence as part of the circumstantial case in that context.
However, regardless of whatever status any lie, or lies, the accused may allegedly have made during his interview with police on 19 September 2019, both sides appear to accept that the proposed DNA evidence forms a significant aspect of the State's circumstantial case.

Analysis of the proposed DNA evidence

In support of the application, and annexed as part of the Outline of Defence Submissions dated 22 August 2025 (Defence submissions), I received the following material:
1.PathWest Forensic Biology Report dated 25 November 2020 prepared by Mr Ross Hedley (PathWest report) annexed as TP1.[15]
2.Forensic Biology Witness Statement of Mr Samuel Cornwell, senior forensic scientist at PathWest, dated 30 November 2023 (Cornwell report) annexed as TP2.[16]
3.Report from Ms Helen Roebuck, principal forensic scientist at Roebuck Forensics, dated 9 May 2025 (Roebuck report) annexed as TP3.
4.An email from Mr Cornwell dated 20 August 2025 in response to matters raised in the defence report (Supplementary Cornwell report) annexed as TP4.
[15] Prosecution brief (PB), page 525.
[16] PB, page 928.
The PathWest report confirms swabs were taken from all eight firearms seized from the unit and tested against the accused's reference sample. The accused's reference sample was the only reference sample provided for testing. With the exception of the swab taken from the Smith & Wesson Magnum revolver which is the subject of count 3, the remaining seven swabs all were reported as having produced a mixed profile that was unsuitable for further analysis due to the complexity of the profile recovered.
I was not referred to any evidentiary material as to how the firearm swabs were taken beyond what was contained in the Roebuck report.[17] No issue was taken with the accuracy of what was described in that report. On that basis, it appears all eight swabs provided to PathWest were taken by WAPOL officer(s) who adopted a process of swabbing the entire surface of each firearm, rather than specific locations on the firearm.
[17] Defence report, page 4, par 7.
Whilst no issue was taken with the accuracy of what was reported, the State did suggest Ms Roebuck's criticism of officers swabbing the firearms in this manner was indicative of a particular 'approach' she had taken when assessing, overall, the adequacy of WAPOL's handling and seizure of the exhibits.[18] Notwithstanding, counsel for the State confirmed Ms Roebuck was not required for cross‑examination[19] and the application proceeded on an apparent acceptance of what was contained within her report. Accordingly, there appears to be no challenge to the credibility of the opinions she offered within the Defence report despite whatever 'approach' she may have adopted.
[18] ts 617.
[19] ts 628.
What is perhaps more significant from Ms Roebuck's criticism of this swabbing method is the consequences that come from it. Because the swabs were taken across the entire surface of each firearm, rather than specific locations, it is likely to have the following consequences:
(a)it increases the likelihood of recovering a mixed DNA sample from multiple sources, and potentially multiple contributors, on the firearm surface;
(b)a greater complexity in any such mixture reduces the prospects of being able to make a reliable comparison;
(c)it eliminates any ability to determine the precise locations on the firearm where particular DNA profiles were deposited; and
(d)there is a reduced capacity to show the implausibility of secondary transfer because of contamination, since it cannot be shown that the identified DNA profiles were absent from areas where secondary transfer might have occurred.

Both the Cornwell and Roebuck reports were prepared for the purposes of offering opinion as to what effect, if any, suggested deficiencies in the handling and seizure of the firearms may have had on the forensic integrity of the exhibits and/or risk of secondary transfer. Secondary transfer, also commonly referred to as indirect transfer, is the process by which biological material containing DNA can be transferred from one person to an object or surface through an intermediate source, as opposed to direct transfer whereby biological material is deposited through direct contact by the donor. Thus, through indirect transfer, a person's DNA can be found on the surface of an object even though that person never physically touched it.
In the Roebuck report Ms Roebuck called the process of causing indirect transfer through exhibit handling as 'investigator mediated contamination' which she described as being:[20]
15.3When an investigator inadvertently contaminates the crime scene (or exhibits) with DNA, this is referred to as investigator mediated contamination.
15.4Investigator mediated contamination can involve introduction of the individual's own DNA into the crime scene. However, this form of contamination is often less problematic as it can often be detected through comparison of the DNA profiles obtained from the crime scene, against databases of police and laboratory staff.
15.5Investigator mediated contamination also includes transferring DNA from one part of the crime scene to another, or from one exhibit to another. For example, this can occur as a result of not changing gloves between each sample collected, or by utilising tools that are not cleaned between exhibits.
15.6Investigator mediated contamination is problematic, as it is not possible to determine through DNA analysis alone whether the DNA profile obtained is from DNA introduced by contamination at the crime scene.
15.7Current DNA analysis methodologies are very sensitive and require only a small number of cells to obtain a DNA profile. Therefore, it is imperative that the investigator takes precautions to minimise the risk of contamination. These precautions are commonly referred to as DNA anti‑contamination precautions.
[20] Defence report, page 7.
Both experts in their reports provide numerous examples of occasions where investigator mediated contamination can be seen occurring during the search of unit 8. Those opinions were based upon a review of what was captured in the approximately 40‑minute audiovisual recording of the search. Having reviewed the recording, I can confirm the accuracy of those descriptions. During oral submissions, the State also ultimately conceded no issue was taken with the observations as to the various failings by WAPOL officers in preserving the forensic integrity of the exhibits.[21]
[21] ts 618.
When commenting on the effect of those failings in the Cornwell report, Mr Cornwell opines:[22]
Whilst the above outlines flaws in the contamination minimisation techniques employed in this instance, there is no expectation that DNA transfer (contamination) has occurred as a result of such flaws. …
[22] Cornwell report, page 7.
With respect to Mr Cornwell, the wording of his opinion was regrettably, and no doubt unintentionally, ambiguous given one possible interpretation of what he has said is that, despite the 'flaws in contamination minimisation', the risk of secondary transfer remained unlikely. Fortunately, that ambiguity was clarified in the Supplementary Cornwell report where he confirmed:
Given the multi‑faceted complexities involved with any DNA transfer event (or contamination event in this case), it is possible that either DNA transfer has or hasn't occurred, however I cannot determine nor do I have an expectation as to which of these two outcomes is true. My position is also that DNA contamination is possible in this scenario given the opportunities for DNA transfer occurring …
Ms Roebuck, in providing her opinion, is both more explicit, as well as more accurately aligned with the evidentiary onus being upon the prosecution. In the Roebuck report, she opines:[23]
The extensive flaws in the crime scene procedure demonstrate numerous pathways for [the accused's] available DNA to have been transferred by officers at the premises. I cannot conclude in these circumstances that contamination of the Smith and Wesson firearm has not occurred.
[23] Defence report, page 11, par 21.
As can be seen, both experts agree that:
(a)flaws in the contamination minimisation techniques were present; and
(b)those flaws have introduced the risk of secondary transfer through the process of investigator mediated contamination.
Because there is no conflict in the opinions offered, no resolution is required. However, to the extent that Ms Roebuck's opinion more accurately reflects the significance of secondary transfer through investigator mediated contamination by reference to the operation of the standard and onus of proof placed upon the prosecution, I prefer and adopt her formulation.
Counsel for the State's oral submissions proceeded on an implicit, if not explicit, acceptance that the way the search and handling of the firearms was conducted did introduce a risk of investigator mediated contamination. However, the State submits that because this crime scene examination involved the investigation of firearms that necessitated the need to make those firearms safe that:[24]
The prospect that you could do that in a completely sterile manner is setting a standard that would be unachievable. …
[24] ts 619.

The State's submission has some merit, particularly given one of the firearms was in fact loaded. But a proper reading of both the Cornwell and Roebuck reports shows that neither author suggests that a 'completely sterile manner' was what was required.
In his report, Mr Cornwell outlines the protocols in place at the PathWest laboratory to minimise the risk of DNA contamination. Both experts accept, and I agree, that such laboratory standards cannot realistically be applied or maintained at a crime scene, given its dynamic and often evolving nature. Necessarily, something less than laboratory standards will apply. But both experts also agree that certain minimum standards will need to be met if the forensic integrity of the evidence is to be preserved.
In the Cornwell report, Mr Cornwell recognises that '[r]egardless of the examination environment, minimum requirements should be adhered to'. Unfortunately, Mr Cornwell does not elaborate upon what those minimum standards require, other than noting they need to apply to the 'use of gloves and clean working environments'.[25] However, the fact Mr Cornwell acknowledges there must be minimum standards to apply to the use of gloves suggests that something more than the mere use of gloves would be required.
[25] Cornwell report, page 2.
This is said much more explicitly in the Roebuck report where Ms Roebuck opines 'the wearing of PPE (e.g. gloves) alone does not, in and of itself, mitigate the risk of DNA contamination'. She provides a clearer indication of what those 'minimum standards' may require when she states that:[26]
The wearing of personal protective equipment (PPE) such as gloves, is one critical procedural step. However, it is imperative that the examiner is continually minded towards minimising DNA contamination throughout their interactions with the crime scene and the exhibits. …
[26] Defence report, page 8, par 15.11.
Undoubtedly, there will be occasions where, even with an officer who remains consistently mindful of minimising DNA contamination, the circumstances of a crime scene examination may provide good reason to depart from the procedures ordinarily required to avoid the risk of investigator mediated contamination. Here, as the State submits, 'there's no getting around' the fact the firearms needed to be made safe.[27] If the evidence was to retain forensic integrity, that process of rendering the firearms safe would have to be done in a way that minimised the risk of investigator mediated contamination.
[27] ts 625.
Assuming officers attended unit 8 without any expectation of locating firearms, it is unclear to me why upon discovering the first firearm, or what was believed to be a firearm, officers could not have suspended the search until the arrival of a suitably qualified forensic officer. Such an officer could then have supervised the continuation of the search and provided guidance on how to preserve forensic integrity while ensuring that any firearm located was rendered safe.
Ultimately, however, for the purposes of resolving the application, I do not need to decide what might be an appropriate procedure that obtains the correct balance between preserving the safety of WAPOL officers and protecting the forensic integrity of the evidence. My role in determining this application is to determine whether the prejudicial effect of the proposed DNA evidence outweighs any probative value it might hold.
With respect to the PEO, if he was 'continually minded towards minimising DNA contamination throughout [his] interactions with the crime scene and the exhibits', the audiovisual recording of the search made clear that the procedures he adopted were not consistent with what was required to avoid investigator mediated contamination. Having reviewed the recording, I accept for all of the reasons as outlined in the Roebuck report, the risk of investigator mediated contamination is real and necessarily affects the reliability and weight to be attached to the significance of the proposed DNA evidence.

Applicable legal principles

The primary rule of evidence is that a court will receive, and only receive, evidence that is relevant to the issues at the trial.[28] Evidence will be relevant if it can rationally affect the jury's assessment of the probability of the existence of a fact in issue,[29] either directly or indirectly.[30] One way evidence may indirectly affect the assessment is if it assists in the evaluation of other evidence.[31] However, if evidence is not relevant, then it is inadmissible. This is not discretionary.[32]
[28] Goldsmith v Sandilands [2002] HCA 31; (2002) 76 ALJR 1024, 1025.
[29] Smith v The Queen [2001] HCA 50; (2001) 206 CLR 650, 654 (Smith).
[30] Roach v The Queen [2011] HCA 12; (2011) 242 CLR 610, 616.
[31] HML v The Queen [2008] HCA 16; (2008) 235 CLR 334, 352.
[32]Smith (650).
Once found to be relevant, the common law rules for exclusion will then apply. The court has a discretion to exclude what would otherwise be relevant and admissible evidence on the ground that its prejudicial effect exceeds its probative value. Examples of where the prejudicial effect may exceed the probative value arise where:
(a)the jury are likely to give the evidence more weight than it deserves;[33] or
(b)the evidence is inherently weak and non‑conclusive.[34]
[33] Festa v The Queen [2001] HCA 72; (2001) 208 CLR 593, 609 ‑ 610 (Festa).
[34] Mukevski v The State of Western Australia [2010] WASCA 138 [35].

Submissions

The accused submits as part of the Defence submissions:[35]
… [I]t would not be possible for a trier of fact to be satisfied beyond reasonable doubt that the DNA of the accused was deposited by direct transfer to the revolver. Accordingly, there is no probative value, which could be derived from the admission of the DNA evidence.
[35] Defence submissions, page 10, par 60.
In oral argument, the submission was developed further with it being contended 'before [the evidence] could go to the jury, the cogency and reliability of that DNA must be established beyond reasonable doubt'.[36] With respect, this submission reflects a conflation between the threshold test for relevance and admissibility with the jury's function as fact finder.
[36] ts 610.
In Baden-Clay the distinction between the role of judge and jury and the functions each were to undertake was made clear:[37]
As a general rule, it will be for the jury to decide, on the basis of the evidence as a whole, whether the post‑offence conduct of the accused is related to the crime before them rather than to some other culpable act. It is also within the province of the jury to consider how much weight, if any, such evidence should be accorded in the final determination of guilt or innocence. For the trial judge to interfere in that process will in most cases constitute a usurpation of the jury's exclusive fact‑finding role.
[37]Baden-Clay (332).
As noted above at [54], the test for relevance is simply whether the evidence can rationally affect the jury's assessment of the probability of the existence of a fact in issue. Whether that evidence is accepted by the jury, what weight to attribute to it and whether it satisfies them in the manner that is contended are all matters for the jury to determine. They are not part of the threshold test of relevance. During oral submissions, counsel for the accused accepted the correctness of this position.[38]
[38] ts 610.
Ultimately, as the submission was developed, the objection appears to be more properly characterised as a complaint that due to the established presence of investigator mediated contamination, the probative weight is so severely diminished that it cannot establish, directly or indirectly, the fact the prosecution invites. Alternatively, the submission is made it would be 'dangerous to convict…because of the significant risk of contamination'.[39] Again, as I understand from this submission, the complaint really is one that the risk is the jury will place undue weight upon what is suggested can be concluded from the DNA evidence, as opposed to what the DNA evidence is capable of establishing.
[39] ts 613.
In response, the prosecution submits:[40]
The weight of the DNA evidence is determined by reference to the objective circumstances. In this case, the secondary transfer argument is a matter that can be out (sic put) to a jury and dealt with by direction as to the intermediate findings that the jury would need to make.
[40] State's submissions, page 2, par 10.
As that submission was developed in oral argument:[41]
… [I]t is ultimately a factual assessment by the jury as to whether or not they accept that there's a real risk [secondary transfer] might have occurred in this case. …
And:[42]
… [T]he State says here that it's for the jury to determine whether or not it's gone over the hill [of proving direct transfer]. And the State says it can get over the hill by pointing to the inherent improbability of that secondary transfer having occurred. …
[41] ts 622.
[42] ts 626.
In essence, the State submits that determining between the two competing inferences, whether the DNA was deposited by direct or secondary transfer, is a matter properly for the jury, and not part of the preliminary exclusionary question as to relevance.

Disposition

The contested facts in issue in this matter are the accused's knowledge and intention to exercise control over one or more of the firearms located within unit 8. To be relevant, the proposed DNA evidence must be capable of rationally affecting the jury's assessment of the probability of the existence of one or more facts underpinning either or both of those issues.
If the jury are satisfied that the component of the mixed profile consistent with the accused's DNA was the result of him directly depositing that material onto the Smith & Wesson Magnum revolver, this could rationally inform their assessment of the likelihood that he had actual knowledge of the firearm's presence in a location under his control. However, if the DNA was not deposited upon the firearm directly, then it appears to have no further relevance. The State has not sought to identify any other uses the DNA may have to the jury's assessment of the facts in issue. Accordingly, as can be seen, the way in which the DNA was deposited upon the firearm is central to its relevance.
Accordingly, the State invites the jury not only to accept that a DNA profile consistent with the accused's was found on the Smith & Wesson firearm, but also to conclude, when considered with the expert evidence on direct and indirect transfer, alongside the other available evidence, namely the evidence of the search captured in the audiovisual recording, that the presence of that profile is only explicable by direct transfer. This is not a question of elevating the significance of the DNA evidence to being a 'link in the chain' as opposed to a 'strand in the rope', it is simply an outline of the only basis this evidence could have bare relevance.
Part of the State's case will consist of the accused's mixed statement containing admissions against interest during which he explained he would use unit 8 to store personal items, such as car parts.[43] There is a plausible basis on which the accused's biological material was already present within the storage unit. This forms part of the assessment of the State's circumstantial case.
[43] PB, page 603.
Taking this into account, along with the lies the accused purportedly told out of a consciousness of guilt, the collective aspects of the State's circumstantial case can establish either of the following scenarios:
(a)Both the accused and Mr Doyle had access to unit 8. The accused used the unit to store his own items including his firearms there. When interviewed about the unit, the accused denied his involvement to distance himself from the fact he knew he stored his firearms there. The accused's DNA profile, later found on one of the firearms, was deposited when he stored the firearm there at an earlier point (the primary scenario).
(b)Both the accused and Mr Doyle had access to unit 8. The accused used the unit to store his own items and knew that Mr Doyle also stored firearms there. When interviewed about the unit, the accused denied his involvement to distance himself from the unlawful storage of Mr Doyle's firearms. The accused's DNA profile, later found on one of the firearms, was deposited not by direct contact but through investigator mediated contamination, transferred from his belongings in the unit during the search on 21 August 2019 (the secondary scenario).
The primary scenario depends on the jury accepting that the DNA was deposited directly. The remainder of the State's circumstantial case, even taken as a whole, does not assist in resolving that issue. While the circumstantial evidence is consistent with the primary scenario, it is equally consistent with the secondary scenario. Accordingly, for the purpose of assessing whether the proposed DNA evidence can rationally influence the jury's determination of whether it was deposited by direct transfer, the remainder of the State's circumstantial case is entirely neutral. Accordingly, the jury's ability to assess whether the DNA profile was placed there through direct transfer or not comes from the DNA evidence itself, assessed in the context of what the jury will be able to determine regarding possible investigator mediated contamination.
The State submits that juries are often required to assess whether DNA was deposited directly or indirectly and, again, that is undoubtedly correct. However, to frame the task as choosing between competing binary inferences, or as deciding whether secondary transfer is plausible or implausible, while a convenient shorthand, risks obscuring the true nature of what the jury must determine in the context of the prosecution's onus and standard of proof. Counsel for the State fairly acknowledged in oral submissions that, at times, the State's argument had been expressed in a way that appeared to reverse the onus, by focusing on the implausibility of secondary transfer rather than considering whether the evidence could plausibly establish direct transfer. This perhaps reflects an unconscious tendency to adopt a process of reasoning that favours direct transfer unless secondary transfer is established as a credible alternative and exposes some of the potential risks with this type of evidence.

To be relevant to the jury's task the jury, after assessing all the evidence, need to accept that the accused's DNA was deposited through direct transfer. As I understand the evidence of both Mr Cornwell and Ms Roebuck, neither go so far as excluding the possibility of direct transfer. Given what I anticipate the expert evidence is likely to be regarding direct and indirect transfer, the proposed DNA evidence is at least capable of establishing the possibility of direct transfer. This satisfies the basal issue of relevance.
However, a jury will still be required to determine whether they accept that evidence. The jury will need to do so in the context of the other evidence they hear. The only other evidence the jury will hear that can inform them regarding the operation of direct and indirect transfer will be from the experts. The jury will then need to apply that evidence when considering and assessing the other evidence in the trial. As noted above, the State's circumstantial case is unlikely to assist to any material degree as it appears intractably neutral on this point.
Consequently, in carrying out a determination of whether they accept that the proposed DNA evidence establishes direct transfer, the only other evidence that can materially assist the jury in that task is what can be seen in the audiovisual recording of the search.
Both experts accept that what is seen in the recording amounts to a possible contamination event that could have resulted in investigator mediated contamination. Both experts agree that from DNA analysis alone, the mechanism by which DNA is deposited, either directly or indirectly, cannot be determined. Both experts can offer their own opinions, based on what is seen in the footage, as to the plausibility or implausibility of direct or indirect transfer.
If what is seen in that recording, when considered in the context of the expert evidence the jury will hear about the risks of secondary transfer and investigator mediated contamination, causes the jury to disregard the proposed DNA evidence regarding potential direct transfer, then this evidence has no further relevance. Up to this point, I agree with the State's submission that this is within the jury's exclusive fact‑finding role as per Baden-Clay.
However, even if, after viewing the audiovisual recording of the search, the jury were to conclude that there is nothing indicating secondary transfer occurred, this would not justify concluding that the DNA profile must have been deposited by direct transfer. To reason in such a binary way would amount to the kind of impermissible reasoning, and reversal of the onus, that I have outlined above.
For the proposed DNA evidence to be relevant to the facts in issue, the jury would still need to consider whether it accepts the evidence that the DNA profile was directly deposited.
The commencement of the recording makes it apparent that various exhibits had already been moved. It is also evident that not only were the exhibits shifted, but so too were crates and other equipment in the storage unit that may have belonged to the accused and potentially carried his DNA. Most, if not all, of the cases containing the firearms appear to have been opened at a time not captured on camera. Given the expert consensus that the procedures visible in the recording fell short of what was required to minimise the risk of contamination, and in fact increased the risk of investigator mediated contamination, there is no basis to assume that the procedures followed off-camera were free from similar shortcomings. The fact the search and removal of relevant items within the unit was conducted in less than 10 minutes reinforces the likelihood this process was not executed in a way that properly maintained the forensic integrity of the exhibits.
As noted above at [2], the purpose of me outlining the history of this matter was not to express criticism, but to highlight the well‑recognised difficulties extended delay will cause to human memory. Those difficulties are compounded further when the witnesses in question are police officers who, undoubtedly since 2019, have carried out countless investigations that would affect their ability to recall with any degree of reliability or precision what procedures and handling occurred off‑camera during the search on 21 August 2019. I am not satisfied the officers would be able to do so in a manner that would be sufficient to allow a jury to reliably make an assessment as to the prospect of direct transfer.
The absence of reliable evidence regarding the handling of the relevant exhibits off‑camera prevents the jury from being in a position where it can properly assess the weight that should be given to the proposed DNA evidence. This inability creates an inherent risk that the jury may attribute greater weight to the DNA evidence than it warrants, giving rise to the kind of unfairness specifically contemplated in Festa, as referred to above.
In my view, this unfairness is contributed to by a combination of the following factors:
(a)The passage of time eliminates any realistic chance of any reliable evidence being adduced that would overcome this prejudice and to allow a jury to carry out a proper assessment of what weight should be attributed to this evidence.
(b)The accused was not present when the search was conducted and so he cannot, from his own account, remedy this deficiency. Regardless, given the passage of time, significant difficulties would attend to the reliability of any purported recollection by the accused.
(c)Because of both the passage of time and the unavailability of any reliable evidence regarding what took place off‑camera, the accused's ability to properly test the evidence that the DNA was directly deposited is lost.
(d)The inability to properly test this evidence further compounds the risk a jury will attach a greater weight to this evidence than what it warrants.
For the reasons I have outlined above, I am satisfied the prejudicial effect of this evidence outweighs the limited probative value it holds, given the risk the jury is likely to give the evidence more weight than it deserves.
To admit this evidence into any trial of the accused would result in an unfairness that cannot be cured by direction. Because of this, the evidence is inadmissible.

Conclusion

The accused's application to exclude the admissibility of the proposed DNA evidence is granted.

I certify that the preceding paragraph(s) comprise the reasons for decision of the District Court of Western Australia.
EO
Associate to Judge Astill
3 OCTOBER 2025