An Australian woman accused of cooking a deadly mushroom meal, admits to picking wild sources, lying to police and disposing of evidence, but will argue that the "tragedy" was "a terrible accident."

Erin Patterson, 50, the Supreme Court trial began Wednesday in the small Victorian town of Morwell and is expected to last for six weeks.

She was charged with murdering three relatives and attempting to murder another, with the case centered on a beef lunch in Wellington and at her home in July 2023.

Ms. Patterson pleaded not guilty, and her defense team said she was "panicked" after accidentally providing poison to her loved ones.

Three people died in the hospital in the days after the meal, including Ms. Patterson's former parents-in-law, Don Patterson, 70, and Gail Patterson, 70, and Gail's sister, Heather Wilkinson, 66.

A lunch guest survived - local pastor Ian Wilkinson was treated in the hospital for weeks.

The court heard that the lunch of Wellington beef, mashed potatoes and mung beans contained death cap mushrooms and caused the guests' illness.

"The overall question is whether she intends to kill or cause very serious injuries," Judge Christopher Beale said.

Prosecutor Nanette Rogers SC said at the opening trial Wednesday that the case was "initially considered a mass food poisoning incident."

But she accused Ms. Patterson of deliberately poisoning "her guests" after inviting them to lunch for lunch after being diagnosed with cancer.

Dr. Rogers said the jury would hear evidence that Ms. Patterson went to her home near Leongatha, where death cap mushroom witnesses had logged in on the Naturalist’s website.

A few days after lunch, she took several steps to "hide" what she did, prosecutors said.

There is evidence that she lied to investigators about the origin of the mushrooms in the dish - saying they came from an Asian grocery store in Melbourne, where she never forages for wild groceries. She went to a local dump to deal with food dehydration prosecutors said she had prepared for toxic meals.

"You might be wondering, 'What's the motivation?' You might still be wondering this is at the end of this trial," Dr. Rogers told the jury.

She explained that the prosecution would not suggest a specific motive.

“You don’t have to satisfy what the motivation is, even a motivation.”

What the jury may hear is testimony from a series of witnesses, she said, including: Mr Wilkinson, Ms. Patterson’s estranged husband Simon Patterson, medical staff treating lunch guests and police officers investigating.

However, the defense reminded the jury in the opening case that they had not heard any actual evidence yet and needed to remain open-minded.

Barrister Colin Mandy said that while prosecutors would try to treat Ms. Patterson's actions as a "crime" after lunch, jurors should consider someone's reaction in this case.

“People might say or do something well thought out…may make them look bad?”

"The defense case was because these four people were sick because she was overwhelmed because she served them. Three people died."

He said Ms. Patterson did not intentionally provide guests with poisoned food.

"She didn't intend to cause any harm that day...what happened was a tragedy, it was a horrible accident."