'It's unexplained': Mystery surrounds poisonous mushroom deaths

Homicide detectives are still trying to work out if a suspected mushroom poisoning, which killed three people, is suspicious or not.

Heather Wilkinson, a local teacher; her sister, Gail Patterson; and Patterson's husband Don Patterson all died after eating toxic wild mushrooms in Leongatha Victoria's Gippsland region on July 29.

A fourth person, Reverend Ian Wilkinson, who is a pastor at Korumburra Baptist Church and Heather Wilkinson's husband, is fighting for life in hospital after also eating the mushrooms at the same meal.

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Detective Inspector Dean Thomas told media today the investigation was "complex" but confirmed a family member was a suspect.

"I would like to say that because the Homicide Squad is investigating this matter, it doesn't automatically mean that the deaths are suspicious," Thomas said.

It's understood the two couples were dining at the home of Erin Patterson, the daughter-in-law of the Pattersons, when they were served the meal.

The home was raided by police on Saturday and the 48-year-old was questioned by police and released pending further investigation.

"She is (a suspect) because she cooked those mushrooms," Thomas said.

Patterson returned to the Leongatha home today, fighting back tears.

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Thomas said the victims' symptoms aligned with those of eating toxic mushrooms known as death caps.

"Lunch was served and the four people left the address," he said.

"Unfortunately late on the Saturday night or early Sunday morning, they came down with symptoms of some type of food poisoning."

Police believe there is "still lots of work to do" for the investigation.

"We need to understand what has caused the symptoms and what has caused the deaths of these three people, and we have a fourth person in a critical condition in hospital," Thomas said.

"We need to understand what has occurred. It's a very complex matter."

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The Victorian Health Department released a warning about death cap and yellow staining mushrooms in April, reporting a spike in the state due to cool and wet conditions.

The health department said it is investigating the incident.

"The department is aware of the situation and our investigations are ongoing," a spokesperson told 9news.com.au.

"We extend our deepest condolences to the patients' family for their loss."

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