Homicide squad detectives are continuing to investigate how four guests became ill after attending a lunch at a Leongatha home in Victoria’s southeast on July 29.

One of the guests, 66-year-old Heather Wilkinson, died in hospital on Friday.

Her husband, 68-year-old Baptist Church pastor Ian Wilkinson, remained in a critical condition at the Austin Hospital on Monday afternoon.

Ms Wilkinson’s sister Gail Patterson, 70, and brother-in-law Don Patterson, 70, have also died in hospital.

The Pattersons’ daughter-in-law, who police say cooked the meal at her home but did not become ill, has been interviewed by investigators.

She was released without charge but police said she remains a suspect.

Outside her Leongatha home on Monday, the woman said she did not know what had happened.

“I didn’t do anything,” she told Nine’s A Current Affair.

“I loved them and I’m devastated they’re gone.”

She declined to answer questions about what meals were served to which guests or the origin of the mushrooms.

Detective Inspector Dean Thomas said the woman was separated from her husband but police have been told their relationship is amicable.

Her children were also at home during the lunch but did not eat the same meal.

The Department of Families, Fairness and Housing has taken the children as a precaution, Det Insp Thomas said.

Detectives searched the woman’s home on Saturday and seized several items.

The type of mushroom the guests ate is unknown but Det Insp Thomas said the symptoms were consistent with those from eating a death cap.

Det Insp Thomas said it would take some time to piece together what happened and police are keeping an open mind.

“It could be very innocent but, again, we just don’t know,” he said.