Victorian police officers have returned to a South Gippsland tip as they investigate the deaths of three people from suspected mushroom poisoning.

Officers were seen speaking to staff at the Koonwarra transfer station, south of Leongatha, today.

The ABC understands police also attended the site on Friday and removed a food dehydrator.

Food dehydrators are used to dry out and preserve fruits, vegetables and meats.

Police have said they are keeping an open mind as they investigate the deaths of married couple Gail and Don Patterson and Ms Patterson's sister Heather Wilkinson.

The three relatives died about a week after sharing a lunch at the Leongatha home of Erin Patterson, who is a daughter-in-law of the Pattersons.

Ms Wilkinson's husband, Ian Wilkinson, remains in a critical condition in hospital.

Police believe the four lunch guests showed symptoms of poisoning by the death cap mushroom, but are waiting for toxicology tests to be completed.

Erin Patterson and her two children, who were at the lunch, did not fall seriously ill.

On Monday, Detective Inspector Dean Thomas said Erin Patterson remained a suspect in the investigation because she had served the meal.

But he added it could be "very innocent … we just don't know".

Shortly afterwards, Erin Patterson told reporters she was "devastated" by the deaths, and "didn't do anything".

"My own children have lost their grandmother," she said on Monday.

"I can't believe that this has happened and I'm so sorry that they have lost their lives."