Erin Patterson has denied deliberately foraging death cap mushrooms and weighing them to calculate the fatal dose for a person, but admitted a series of lies to police as homicide detectives investigated the fatal lunch.

On her fourth day in the witness box, Patterson’s cross examination started, and the jury was told the estimate for the trial had blown out by at least a fortnight.

Patterson, 50, faces three charges of murder and one charge of attempted murder relating to poisoning four in-laws with beef wellington served for lunch at her house in Leongatha on 29 July 2023.

Patterson has pleaded not guilty to murdering her estranged husband Simon’s parents, Don and Gail Patterson, and his aunt Heather Wilkinson, and attempting to murder Ian Wilkinson, Simon’s uncle and Heather’s husband.

Early in her cross-examination by prosecutor Nanette Rogers SC, Patterson was shown images of mushrooms on scales.

She agreed the photos appeared to have been taken by her in her home.

Rogers told Patterson that Dr Tom May, a mushrooms expert who gave evidence earlier in the trial, identified with a high degree of confidence that the images showed death cap mushrooms.

Rogers suggested to Patterson that an image of sliced mushrooms on a dehydrator tray placed on scales showed death caps she picked on 28 April 2023 in Loch. A public post on iNaturalist earlier that month identified them growing there, and the exact location.

“I suggest you were weighing these death cap mushrooms so that you could calculate the weight required to calculate the administration of a fatal dose for one person,” Rogers asked Patterson, before also suggesting that she calculated the weight required for fatal doses for five people.

Patterson denied both suggestions.

Under questioning from her lawyer, Colin Mandy SC, earlier on Thursday, Patterson said she repeatedly lied to police during her interview with detectives on 5 August about her food dehydrator.

The dehydrator was later recovered at a local tip with her fingerprints on it, and with traces of death cap mushrooms on it.

“And why did you tell the police those lies on the 5th of August?” Mandy asked.

“Well I had disposed of it a few days earlier, in the context of thinking that maybe mushrooms that I’d foraged or the meal I’d prepared was responsible for making people sick,” Patterson responded.

“And then on the Saturday, Detective Eppingstall told me Gail and Heather had passed away, and it was this stupid kneejerk reaction to just dig deeper, and keep lying.

“I was just scared. But I shouldn’t have done it.”

Justice Christopher Beale told the jury that it was expected the trial would continue for at least two more weeks , with Patterson’s evidence possibly stretching into next week.

The trial continues.