The jury in the high-profile murder trial of an Australian woman accused of cooking a deadly mushroom lunch for relatives has retired to decide her fate.

Erin Patterson, 50, has pleaded not guilty to four charges – three of murder and one of attempted murder – over the beef Wellington lunch at her regional Victorian house in July 2023.

The prosecution have claimed Ms Patterson knowingly put toxic death cap mushrooms into the home-cooked meal, before lying to police and disposing of evidence.

But the defence argue Ms Patterson accidentally included the poisonous fungi in the dish and only lied because she panicked after hurting people she loved.

Ms Patterson’s in-laws, Don and Gail Patterson, both 70, along with Gail’s sister Heather Wilkinson, 66, all fell ill and died days after the lunch in Leongatha.

Heather’s husband, local pastor Ian Wilkinson, recovered after weeks in an induced coma. Simon Patterson, the accused’s estranged husband, had been invited to the lunch too, but pulled out the day before.

On Monday, Justice Christopher Beale gave his final instructions to the 14-member jury, summing up evidence from the prosecution and the sole defence witness, Ms Patterson.

After almost two months and more than 50 witnesses, the final 12 jurors were decided by a ballot before the group retired for deliberations.

In her closing arguments, prosecutor Nanette Rogers SC said Ms Patterson has “told so many lies it’s hard to keep track of them”.

The prosecution alleged Ms Patterson lied to her relatives about a cancer diagnosis to convince them to attend the fatal lunch, poisoned them and then faked an illness to cover her tracks.

Ms Patterson’s further lies to police and medical staff about foraging for wild mushrooms, as well as her decision to dump a food dehydrator used to prepare the meal, were evidence of her guilt, they argued.

“She has told lies upon lies because she knew the truth would implicate her,” Nanette Rogers said.

“When she knew her lies had been uncovered, she came up with a carefully constructed narrative to fit with the evidence – almost.”

There was no “particular motive” for the alleged crime, Dr Rogers told the court, but the jury should still have “no difficulty” in rejecting the argument “this was all a horrible foraging accident”.

However, the defence argued the lack of motive was key. Ms Patterson had no reason to kill her guests, they said.

During Ms Patterson’s evidence, she told the jury she was very close to her in-laws and never intended to harm them.

As she was preparing the lunch, Ms Patterson claimed she added mushrooms from a container in her pantry that she now realised may have included both store-bought and foraged mushrooms.

She also told the court she had suffered from bulimia for years, and had made herself throw up after the beef Wellington meal – something her defence team says explains why she did not become as sick as the others who ate it.

The lie about having cancer was because she was embarrassed about plans to get weight-loss surgery, Ms Patterson said, and she didn’t tell authorities the truth about her mushroom foraging hobby because she feared they might blame her for making her relatives sick.

“She’s not on trial for lying,” defence lawyer Colin Mandy SC, “this is not a court of moral judgment”.

He accused the prosecution of trying to force “puzzle pieces” of evidence together, “stretching interpretations, ignoring alternative explanations because they don’t align perfectly with the narrative”.

In his final instructions, Justice Beale told the jury members they alone are the “judges of the facts in this case”.

He said they should not convict Ms Patterson simply for lying, as there are “all sorts of reasons why a person might behave in a way that makes the person look guilty”.

He added that while “any reasonable person would feel great sympathy” for the Patterson and Wilkinson families, jurors also must not allow themselves to be swayed by emotions.

The jury has now been sequestered, which means that while they deliberate, they will stay in supervised accommodation where they will have little to no contact with the outside world until they have reached a decision.