In this image from a video, Victoria Police Detective Inspector Dean Thomas speaks during a press conference in Melbourne, Aug 7, 2023. Australian police on Aug 9 were trying to figure out how three people died and a fourth became critically ill after apparently eating wild mushrooms at a family lunch. (PHOTO / AUSTRALIAN BROADCASTING CORP. VIA AP)

SYDNEY - Australian police were on Thursday investigating the deaths of three elderly people who died after allegedly consuming mushrooms at a lunch two weeks ago.

Don Patterson, his wife Gail Patterson and her sister Heather Wilkinson, became ill and later died after the lunch on July 29 in Leongatha, a small rural town around 135 km southeast of Melbourne, police and local media said.

A fourth man, Wilkinson's husband Ian Wilkinson, a pastor in a nearby town, remains in critical condition in hospital.

Deaths from consuming mushrooms are relatively rare in Australia, which has several species including the "death cap" mushroom that are dangerous enough to poison and kill a human

The mysterious deaths have gripped Australia, with interest only increasing after police on Wednesday searched a local refuse center for a dehydrator believed to have been used in the preparation of the lunch.

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On Sunday, police said they had questioned a 48-year-old woman who served the lunch before releasing her without charge.

"What happened is devastating and I'm grieving too," the woman told media in a tearful interview outside her home on Monday.

The investigation is likely to be lengthy due to the complexity of the case, Detective Dean Thomas said on Monday.

"We presume at this stage it was mushrooms but it's a complex investigation that I think will take some time," he said.

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The Patterson and Wilkinson families said in a statement in a local newspaper on Sunday they were grateful "to our wider communities for their outpouring of love, support, and prayers."

"This support extends not only to those we have tragically lost but also to our family member who continues to bravely fight for his life in the hospital."

Deaths from consuming mushrooms are relatively rare in Australia, which has several species including the "death cap" mushroom that are dangerous enough to poison and kill a human.

The deaths have led to warnings from health experts across the country not to forage for wild mushrooms and to buy from reputable sellers.