Erin Patterson, the Australian woman who cooked the mushroom meal that killed three people, says she is being painted as an 'evil witch' by the media.

A former homicide detective has opened up about investigators’ next moves as they look to break the fatal mushroom lunch case that killed three people wide open.

On July 29, Erin Patterson cooked a beef wellington lunch at her home in Victoria for her former in-laws Don and Gail Patterson, along with Gail’s sister Heather Wilkinson and her husband Ian Wilkinson.

However, the lunch turned deadly when Don, Gail and Heather all died after eating the meal, which allegedly contained death cap mushrooms.

Patterson’s former husband Simon was supposed to be at the lunch but had to pull out at the last minute.

Earlier this week veteran crime reporter John Silvester claimed police forensics had proven poisoned mushrooms caused the deaths.

Now former Victoria detective Charlie Bezzina told Daily Mail Australia there are likely to be further twists with police likely to make new moves that could unlock the entire case.

He said if Silverster’s claims are true, then five key areas of investigation will need to be examined before charges can be laid.

To date, no charges have been laid and police have not suggested Patterson intended to harm or kill anyone.

Bezzina said the key will be what Pastor Wilkinson has told detectives given he survived the deadly lunch.

“Pastor Wilkinson can say if the guests were invited over to (Erin Patterson’s) house, say, every Sunday, every fortnight or month, or if they hadn’t been invited over previously,” he told Daily Mail Australia.

“As investigators, we don’t prove innocence or guilt, we present fact that is either inculpatory or exculpatory (tending to incriminate, or tending to clear guilt).”

With that in mind, Bezzina laid out what they’re be focusing on at police headquarters.

THE FATAL LUNCH

He said the key questions that will be posed will be why the lunch was held, what was the customary “course of conduct” and behaviour like between Patterson and each individual guest.

Bezzina said Pastor Wilkinson’s information on how the lunch was served, if he knows how it was prepared, where it was prepared or whether any further discussion around mushrooms took place, will be vital in painting the atmosphere of the lunch and that could help lead police on the path to the truth.

Was there a second party involved?

The former detective said Wilkinson might be able to help work out whether someone else helped prepare the meal and given it to Patterson who unknowingly served it, or whether there was any motive or reason to harm the lunch guests.

Bezzina said this could take years to come to a conclusion, especially given there is just one sole survivor not including Patterson.

Where the deadly fungi came from

It will be vital in discovering where the poisonous mushrooms came from and how they ended up in the pie.

Police located and seized the mushroom dehydrator Patterson discarded at the local rubbish dump, in a panic, she describes. They would have also collected evidence from her house.

While the dehydrator may not pick up evidence of mushroom as it may have been washed, other household kitchen items might contain fragments of the deadly mushroom for investigators to delve into.

“You need to find out how the (Death Cap mushrooms) came to being cooked in the meal, but it will be important to take samples from kitchen surfaces and cooking utensils to prove beyond doubt they were there, should this go to court,” Bezzina said.

They would also be establishing whether areas nearby her town facilitate the growth of Death Cap mushrooms. He said investigators will also be speaking to Melbourne University and toxicologists and botanists.

Is Patterson’s story true or false?

Patterson told police she was hospitalised herself following the lunch. He said police will check hospital records to stack up Patterson’s report as well as look into the treatment and results of any tests.

She also said she purchased the mushrooms from an “Asian grocery store” and police will need to investigate whether that claim is correct.

While she can not remember which store, police will be hopeful she can tell her what area so they can check CCTV to confirm her account.

“Saying she doesn’t remember where the Asian shop is doesn’t make her a killer, as she said, after the deaths she was feeling so devastated.”

“But the investigators will run rabbits down every burrow.”

Patterson’s ex-husband and children

Her relationship with her ex-husband and children could be a key detail of the police’s probe.

Patterson said she loved her family and so what could she have to gain if they died, Bezzina stressed.

Both her ex Simon Patterson and her children will be interviewed, and past events or controversies would be examined.

A bizarre death wall of graffiti showing tombstones was allegedly drawn by the children. They will likely be asked about that as well as Simon’s time in hospital a number of years ago where he fell sick and nearly died after eating food from Patterson.

A coronial inquest to be completed

A coronial inquest could help police determine what happened.

The investigation is ongoing.