By Paul Gregoire and Ugur Nedim
Western Australian police officers executed a search warrant on 21 August 2019, on the number 8 storage unit at Billabong Self Storage facility located on Cutler Road in the Perth suburb of Jandakot. The search was carried out in front of Darcey Doyle, who was one of two people the content of the storage unit belonged too, with Tommaso Piccioni, the other individual, not then present.
Parts of the search were recorded audiovisually. Officers located a number of firearms, revolvers and ammunition, amongst stored goods, such as car parts. One box contained two rifles, another stored a Zoraki 9 mm pistol, while a third held a Smith & Wesson Magnum revolver, and in the same box was another pistol. Three different types of ammunition were also strewn about the unit.
Doyle and his co-accused Piccioni were then charged with a number of firearm offences on 14 October 2019. The state moved to proceed against Doyle alone initially, and this led to five of seven charges against him dropped in August 2024, with the remaining two then dismissed in September this year. Indeed, no DNA evidence had been located at the storage unit linking Doyle to the guns.
The state continued against Piccioni, however. And prior to his standing trial in late October 2025, his matter went before the WA District Court to deliberate on a preliminary question as to whether a piece of DNA evidence, specifically PathWest testing swab F0915160-0, should be permitted as this was a ‘mixed profile’, with four different contributors, one of which had been identified as Piccioni.
The question before the court on 18 September 2025 was whether the specific DNA sample should be admissible, in terms of the potential prejudicial effect of admitting it outweighing the probative value it could have, due to the “mass contamination” that was involved in the search of the storage unit, which occurred as the seizure of evidentiary material was done incompetently.
Charges before the court
Both Doyle and Piccioni were charged with seven crimes. By the time the admissibility of evidence question came before the WA District Court, however, only Piccioni remained charged.
At the time of the September hearing, Piccioni continued to face four counts of unlawfully possessing a firearm, contrary to section 213 of the Firearms Act 2024 (WA), which is a crime that carries up to 5 years gaol time and a fine of $60,000.
The accused was also continuing to face three counts of unauthorised possession of ammunition, contrary to section 241 of the Firearms Act. This offence carries up to 3 years imprisonment and a fine of $36,000.
A circumstantial case
WA District Court Judge Craig Astill explained, during the hearing on the admissibility of DNA evidence, that the case was circumstantial, meaning that it relied on indirect evidence and the judicial officer would have to make an inference to find guilt, rather than directly observe evidence. And his Honour added that the DNA evidence formed “a significant part of” the case.
In its submission to the court, the state of WA underscored that the DNA evidence was complementing “an existing circumstantial case and is not an indispensable link in the chain of reasoning”. The DNA evidence assisted in establishing that Piccioni had direct access to unit 8 at Billabong Self Storage, however this was not the sole indicator of this.
To establish that Piccioni had possession of the guns and ammunition, the state relied upon the DNA evidence, and that the accused told lies when questioned which were later considered to have had to be motivated by a guilty conscience, as well as further post offence conduct that comprised of cleaning out unit 8 the month after the raid.
His Honour explained that the post offence incriminating conduct, which included the lies and the clearing out of the storage unit, are examples of circumstantial evidence. The defence added that cleaning out the unit could also imply the facility had requested the accused do this because ownership of the storage unit was being terminated.
However, a jury does not have to be satisfied beyond a reasonable doubt to establish guilt in terms of post offence behaviour. That is unless the specific evidence is an indispensable part of a chain of circumstantial evidence pointing to guilt. If a piece of circumstantial evidence is required to prove guilt, then that specific item of evidence must be proven beyond a reasonable doubt.
The DNA evidence
Four separate forensic analyses of the DNA evidence were before the court. A PathWest report outlined that eight tests from various firearms were tested against Picconi’s sample. All samples, except for that taken from the Smith & Wesson, were mixed profile and unsuitable for further analysis. And WA police officers took swabs of the entire firearms, rather than of specific locations.
The analysis of principal forensic scientist at Roebuck Forensics, Helen Robuck, criticised the swabbing technique applied by police, as swabbing an entire item increases risk of mixed sample, while testing specific locations results in more accurate readings. The WA police swabbing was incapable of indicating whether Piccioni’s specific DNA had been directly deposited on the firearm.
Roebuck and a further analysis by a Mr Cornwell found that “investigator mediated contamination” had taken place in respect of the sample. This occurs when an investigator contaminates a sample with their own DNA, without actually directly touching the object. Investigator contamination, however, is not as problematic as inadvertent transfer of other crime scene DNA.
Cornwell and Roebuck both included “numerous examples of occasions where investigator mediated contamination can be seen occurring during the search of unit 8”, based on a 40-minute clip of the search. And Judge Astill confirmed that he’d also watched the footage and observed the instances of contamination.
Counsel for the state of WA accepted that some level of the investigator mediated contamination had occurred, but the search had to take place, and complete sterility was impossible in the circumstances. But the experts hadn’t called for complete sterility, rather certain laboratory standards could have been adhered to, even though they could not be completely replicated.
Roebuck cited ‘minimum standards’ in her report, and as an example she provided the use of PPE (personal protective equipment) gloves.
His Honour suggested that while the investigating officers might not have been expecting to come across firearms during the raid, from the point of discovery of the first gun, he considered that the investigation should have been paused to await the assistance of a forensic expert.
“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,” Judge Astill made clear.
Inadmissible at trial
His Honour then explained that if evidence is found not to be relevant, then it is considered inadmissible, and this is not a discretionary conclusion, as the common law principle of exclusion applies. But if evidence has been found relevant, the court then has to take a discretionary option to exclude it, when “its prejudicial effect exceeds its probative value”.
If the accused’s DNA found on the Smith & Wesson was understood to be directly deposited on it, when it was held in a storage room in Piccioni’s control, then it could be inferred he was aware that it was stored there. However, if the DNA was not directly deposited, it ceases to hold its relevance to the case.
The Roebuck and Cornwell advice does not ultimately rule out indirect deposit of DNA onto the revolver. If the DNA evidence remained, a jury would still have to rule on whether it was permissible. The only evidence as to whether this was the case is the audiovisual from the search, which does show possible indirect contamination. And this footage neither indicates what occurred off camera.
The risk his Honour then identifies is that a jury might place too much weight upon the DNA evidence, which would lead to unfairness. Four factors heighten this possibility: the passage of time since the incident, that Piccioni was not present at the search to elaborate, there is no evidence as to what did take place off camera and this all leads to an inability to properly test the evidence.
“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,” Judge Astill set out on 3 October 2025.
“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,” his Honour said in handing down his determination.
“The accused’s application to exclude the admissibility of the proposed DNA evidence is granted.”
