CriminalThe Achilles’ Heel of the Prosecution: Chain of Custody Issues in the Erin Patterson Trial

In Australia’s most closely watched murder trial of 2025, prosecutors have presented compelling forensic evidence linking Erin Patterson to the death cap mushroom poisonings that claimed three lives. Yet beneath this seemingly robust case lies a procedural vulnerability that legal experts predict will almost certainly form the centerpiece of any post-conviction appeal: the questionable chain of custody for the beef Wellington leftovers at the heart of the prosecution’s case.

The case against Patterson hinges on leftovers from a July 2023 lunch where she allegedly served death cap mushroom-laced beef Wellington to four relatives. Three died—Don and Gail Patterson and Heather Wilkinson—while Ian Wilkinson survived after weeks in hospital. Patterson has pleaded not guilty to three counts of murder and one of attempted murder.

Victoria’s chief toxicologist Dimitri Gerostamoulos testified that samples from the leftovers tested positive for death cap mushroom toxins. This evidence appears damning—until one examines how these samples were handled.

Recent testimony has revealed a troubling sequence of events in the evidence collection process. Leftovers were collected from two different locations in Patterson’s home but combined into a single bag—a practice Gerostamoulos himself characterized as “not an ideal way to receive the samples.” This admission from the prosecution’s own expert witness creates a significant vulnerability.

The timeline raises further questions. The Victorian Institute of Forensic Medicine received these samples on August 29, 2023—a full month after the fatal lunch. Plant virologist David Lovelock testified he received samples on August 2, indicating the evidence passed through multiple facilities and handlers during this critical period.

For sophisticated observers of criminal proceedings, these details aren’t mere technicalities—they strike at a fundamental principle of forensic evidence. Chain of custody documentation must establish, without gaps, that evidence presented at trial is identical to that collected at the scene and has remained uncontaminated.

The National Institute of Justice defines chain of custody as “a recorded means of verifying where the evidence has travelled and who handled it before the trial.” This unbroken chain ensures that crucial evidence hasn’t been tampered with, contaminated, or misidentified.

When evidence passes through multiple hands, facilities, and storage conditions—particularly when combined from different sources into a single container—defense attorneys gain powerful ammunition to challenge its reliability.

The Patterson case bears striking parallels to Australia’s most notorious miscarriage of justice—the 1982 conviction of Lindy Chamberlain for the alleged murder of her nine-week-old daughter Azaria. Chamberlain maintained that a dingo had taken her baby from their tent at Uluru, but forensic evidence purportedly showing fetal blood in the family car led to her conviction and imprisonment.

In a dramatic vindication, the High Court of Australia ultimately overturned Chamberlain’s conviction after new evidence emerged and the original forensic findings were discredited. The supposedly damning blood evidence was later determined to be a combination of copper dust, sound-deadening compound, and other manufacturing materials—not blood at all.

The Chamberlain case stands as Australia’s most powerful reminder that even seemingly conclusive forensic evidence can be fatally flawed. Significantly, as in the Patterson case, the original hard forensic evidence in the Chamberlain trial was compromised before proper independent analysis could be conducted.

Should Patterson be convicted, her defence team will almost certainly cite these chain of custody issues as grounds for appeal, following the Chamberlain precedent. The strategy writes itself: How can a jury rely on evidence that was improperly collected, combined from different locations, and passed through multiple handlers over a month-long period?

While Gerostamoulos testified that his facility is accredited, meaning “the integrity of the results could withstand scrutiny,” this professional assurance may not overcome the procedural flaws in how the evidence was initially collected and handled before reaching his laboratory.

Australian courts have previously overturned convictions based on chain of custody issues. In cases where forensic evidence forms the cornerstone of the prosecution’s argument, appellate courts—particularly the High Court—apply particularly rigorous scrutiny to evidence handling procedures, as demonstrated in the Chamberlain case.

The commingling of samples from different locations, the month-long testing delay, and the toxicologist’s admission of suboptimal handling create a perfect storm of appealable issues. These aren’t minor procedural missteps but fundamental challenges to evidence integrity.

This case highlights a persistent tension in criminal prosecutions: the balance between scientific certainty and procedural integrity. Even when forensic testing yields seemingly conclusive results, procedural flaws in evidence collection and handling can undermine their legal weight.

For prosecutors, the lesson is clear: meticulous documentation and handling of evidence is not merely best practice—it’s essential to securing convictions that withstand appellate scrutiny.

For the Patterson case specifically, the prediction is straightforward: if convicted, an appeal based on chain of custody issues is not merely possible but probable, with a reasonable chance of success given the documented handling concerns and the Chamberlain precedent.

As this high-profile trial continues, the prosecution’s forensic evidence may convince a jury, but the procedural questions surrounding its collection and handling have already laid the groundwork for what many legal observers see as an inevitable and potentially successful appeal—potentially adding another chapter to Australia’s history of convictions overturned due to flawed forensic procedures.