Mushroom trial: Motive and murder - what the jury must decide

With all evidence now complete, closing arguments are underway in one of the most high-profile murder trials in Australia. But jurors in Victoria aren’t being asked to find a motive. They’re being asked to decide whether Erin Patterson is guilty of murder beyond reasonable doubt.

Experts agree the legal threshold is one of the most misunderstood elements of criminal trials - so what does that actually mean? Australia Correspondent Aziz Al Sa'afin explains.

Speaking to 1News, Criminal barrister Rishi Nathwani KC explained it like this: “It doesn’t mean beyond any doubt at all - just beyond a reasonable one. If the jury finds there is a real possibility the accused is innocent, they must acquit.”

Nathwani said while the phrase remains in use in Victoria, in other jurisdictions it’s sometimes simplified as: “Are you sure?”

If jurors are not sure, based on the evidence presented in court, then the verdict must be not guilty.

The Crown has alleged Erin Patterson deliberately served a meal containing death cap mushrooms that killed three of her relatives and left a fourth man fighting for life. But prosecutors have explicitly told jurors not to focus on motive.

“You don’t need to find a motive to find someone guilty of murder,” the prosecution has said.

Instead, they argue that Patterson’s behaviour - including her shifting explanations, deleted data and acquisition of a food dehydrator point to intent.

In closing arguments, Patterson’s barrister Colin Mandy SC warned the jury not to judge her through the lens of hindsight.

“This trial isn’t about what might have happened. It’s about what the evidence shows.”

He said much of the Crown’s argument is based on “speculation” and assumptions that don’t amount to proof.

Under Victorian law, jurors must decide whether Erin Patterson:

That’s it.

Even without a clear motive, even with odd behaviour - Nathwani said if there’s a reasonable explanation that fits the evidence, Patterson must be acquitted.

Over the course of the trial, the Crown argued:

The prosecution also suggested the sixth beef Wellington - prepared for her estranged husband - was kept separate and potentially safe, though he did not attend the lunch.

The defence has said:

They also say surviving guest Ian Wilkinson - who testified the accused used different coloured plates - was “honestly mistaken”.

They raised the possibility a third, unknown mushroom species may have been present in the leftovers, citing expert testimony from a virologist.

In Victoria, murder charges require a unanimous verdict. Justice Beale will try to avoid a hung jury by directing the jury to continue deliberating and try to reach agreement. But it is possible it could result in a mistrial if all options have been "exhausted".

As Nathwani explained: “The judge would, if [the jury] made it aware they were struggling to reach a unanimous verdict, direct them... There’s a direction he can give of law, which says, you know, you’ve got to listen to each other... But if they can’t, then it’s a retrial, and they do it all again in many months’ time.”

Week 1–2: Opening arguments and early witnesses, including police and hospital staff.

Week 3: Toxicology and forensic experts testified on the symptoms of death cap poisoning.

Week 4: Phone and tech evidence, including the factory reset, was presented.

Week 5: Botanical and mushroom experts, including Dr Tom May, confirmed death cap DNA in cooking equipment.

Week 6: Testimony from Patterson’s children and others about her behaviour.

Week 7: Erin Patterson testified across eight days. She denied intent and maintained it was a tragic accident.

Week 8: Closing arguments. Prosecution accused her of inventing key parts of her story. Defence said speculation and hindsight are not proof.

Judge Christopher Beale is expected to give final directions to the jury next week. Deliberations could begin by the end of June.