Erin Patterson and the art and science of poison

As the world now knows, Erin Patterson’s weapon of choice is the death cap mushroom – the potent, naturally harvested amanita phalloides.

But what has been a secret until now is that it wasn’t the only deadly option she considered.

The story of how the 50-year-old mother of two came to select amanita phalloides can only be told now, following a decision by the Supreme Court of Victoria on Friday to drop a suppression order preventing any publication of information that was revealed in a series of pre-trial hearings in 2024.

These hearings contained information gathered by Victoria Police for Erin’s upcoming trial on three counts of murder for Don and Gail Patterson and Heather Wilkinson, and one count of attempted murder of Ian Wilkinson, as well as three separate attempted murder charges for allegedly poisoning her estranged husband, Simon Patterson.

Those attempted charges were dropped before the start of her trial in late April for reasons that have not been publicly disclosed.

They relate to three incidents in 2021 and 2022 when Simon was hospitalised with mysterious, never-explained illnesses after allegedly eating meals prepared by Erin, including penne bolognese, chicken curry korma and vegetable curry wrap.

Most of the meals were prepared and served by Erin either before or during a series of camping trips the pair had planned to go on together, and caused Simon to experience symptoms so severe he spent several days in a coma and had part of his bowel removed during one of the hospital stays in 2022.

It can now be revealed that in two separate search warrants executed at her home in August and November 2023, police seized multiple electronic devices – desktop computers, laptop computers, tablets, phones and SD cards – that contained a wealth of information about poisons as part of a deep dive into the subject that went back nearly four years before the fatal lunch.

The evidence – none of which was ever shown to the jury due to a series of pre-trial rulings by Supreme Court Justice Christopher Beale – paints the picture of a person obsessively focused on the nature and use of poisons.

In 2019, Patterson apparently downloaded a portion of a book called Criminal Poisoning: Investigational Guide for Law Enforcement, Toxicologists, Forensic Scientists and Attorneys.

It was an all-encompassing manual on the theory and practicalities of using poison to kill, including the psychology of those who use it and how the crimes are investigated by authorities.

The chapter in question that was found on her computer was a list of common homicidal poisons, from anti-freeze to arsenic, cyanide and strychnine.

Scientific and academic articles with a very specific focus on poisonous substances were also found on her devices, including Red Kidney Bean Poisoning in the UK and One Step Purification and Characterisation of Abrin Toxin from Abrus Precatorius Seeds.

Both of these poisons can be derived from plants that are found widely in Australia.

But they weren’t the only potentially lethal suspects investigated by police, who cast a wide net looking for possible explanations for what might have caused Simon’s suite of similar but distinct illnesses.

During the homicide probe, toxicology expert Dr Dimitri Gerostamoulos was brought in to consult on obscure poisons made famous from history and the War on Terror that Erin might have used on Simon’s food.

“I was asked to prepare those [by investigators],” Gerostamoulous testified during pre-trial witness examinations in October 2024.

The first was on hemlock, which history buffs will recognise as the poison made famous by Athenian philosopher Socrates to take his own life in Ancient Greece.

Hemlock, indigenous to Europe and Africa, is a highly poisonous flowering plant that has spread to Australia and become prevalent enough in “disturbed soil areas” like roadsides to be classified as a noxious weed.

The second, ricin, is a poison distilled from castor beans that became a subject of public fear in the Cold War for its use to assassinate spies. It was also used as bioweapon in the War on Terror after the 9/11 attacks. In April 2013, ricin was mailed to US President Barack Obama and a senator, shutting down the postal service in the US.

Simon’s close mate, Bible study partner and GP Christopher Ford also weighed in with a suggestion that was raised during pre-trial hearings – that Erin could have slipped anti-freeze into a batch of cookies made for Simon by their daughter.

Ford told the court Simon had been apprehensive about eating the batch after Erin called several times to ask whether he had eaten any yet. He said the father of two eventually had a small nibble before throwing the rest out.

None of these would pan out.

But Victoria Police would continue to search for other possibilities, even up to the eve of her trial.

Even as late as early April 2025 – just weeks before her triple-murder trial was set to begin in Morwell – the prosecution toyed with introducing newly discovered forensic evidence relating to digital traces found on Erin’s computers that linked to barium carbonate, also known as rat poison.

“There was an article on barium carbonate (rat poison) that was discovered by the Crown around the time that [Simon Patterson got sick for the third time],” prosecutor Dr Nanette Rogers told the Court of Appeal.

“Barium carbonate is a rat poison. Professor [Andrew] Bersten has provided a further report, which we’ve served on the defense, which indicates that the sudden onset of illness for charge three is consistent with barium carbonate poisoning.”

Then there were the now-infamous death caps.

The electronic evidence showed Patterson’s interest began to narrow down to mushrooms in general and then death caps in particular.

In 2022, she downloaded a copy of An Overview of the Fungi of Melbourne, which was a technical guide on local mushroom species written by preeminent mycologist Dr Thomas May of the Royal Botanic Gardens.

That same year, computer records show she was surfing the iNaturalist website looking at sightings of death caps in suburban Melbourne, including one in a Moorabbin nature reserve.

And, as the prosecution would make clear during testimony at the trial, Patterson took at least three ‘foraging’ trips to locations where death caps have been observed and posted on the iNaturalist website in the months leading up to the fatal lunch.

Out of order

This intense and sustained interest in poisons was “not a one-off”, the prosecution argued.

But the jury in Patterson’s murder trial in Morwell heard hardly any of this digital evidence, beyond her forays onto iNaturalist.

In his pre-trial rulings, Supreme Court Justice Christopher Beale ruled nearly all of this electronic-sourced material as inadmissible because it was unfairly prejudicial against the accused.

It was also unclear, according to the judge, that Patterson had actually opened or read some of these materials because only incomplete traces of the files were sometimes found.

At trial, defence barrister Colin Mandy, SC, also pointed out that despite police seizing at least 423 books from her home and a storage locker, there would not be a single one found about poisons.

The prosecution countered that there also were none about foraging for wild mushrooms, which Erin testified had become a foodie passion project in the lonely years of the COVID pandemic.

If Patterson had downloaded and accessed these materials in full, it’s quite possible she would have found an insight into her own thinking buried deep inside Criminal Poisoning: Investigational Guide for Law Enforcement, Toxicologists, Forensic Scientists and Attorneys.

She would have read that homicidal poisoners are often motivated by revenge, financial gain or political ambition. She would have noticed a diagram denoting a skull-and-crossbones symbol – the universal symbol of toxic substances – showing what motivates poisoners and who their victims are.

But perhaps the most illuminating detail for the convicted murderer in that chapter, had she stumbled across it, would have this single sentence: “One of the major reasons [murderers choose poison] is that it provides a very good chance of getting away with the crime.”

While the vast majority of the evidence documenting her deep interest in poisons never made it to trial, what did was clearly enough for the jury.

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