Criminal experts have described mushroom killer Erin Patterson as a “formidable witness” who “knew what she was doing”.

Patterson this week was convicted of three counts of murder and one count of attempted murder, following a mammoth 10-week-long trial.

The 50-year-old’s estranged husband Simon’s parents, Don and Gail Patterson, 70, and aunt Heather Wilkinson, 66, all died in hospital days after Patterson served them beef Wellington parcels laced with death cap mushrooms in July 2023.

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Heather’s husband, Ian Wilkinson, was the sole survivor.

Now, in a 7NEWS Spotlight special, presenter Michael Usher investigates how the seemingly ordinary mother-of-two became one of the worst female mass murderers in Australian history.

Featuring in-depth analysis and expert commentary from industry leaders including criminal barrister Geoffrey Watson, forensic psychologist Peter Ashkar and former detective Damian Marrett, Spotlight dives into the mind of a killer.

According to Usher, Mr Ashkar described poisoning someone as an “act of aggression” and said it was a “very deliberate act of control of power”.

“(Being poisoned) is an absolutely hideous way to die because there’s intense pain and suffering,” Usher said.

Mr Ashkar also described Patterson as smart and cunning and said “she knew what she was doing”.

“If you look back at the vision of her at her home when our reports went and door-stopped her, (she was) in tears and was distraught and upset,” Usher said.

“But on the stand, Ashkar said she was formidable — she knew what she was doing and she was clear and smart.

“(Ashkar said Patterson) knew what was going on, she was in charge and she owned her narrative.

“Getting inside her mind is a fascinating and frightening exercise.”

But Usher said Patterson didn’t appear to have a clear motive.

“We’re so used to murder cases (where there is a) very clear motive like revenge, fame or money,” he said.

“It’s not like she had a proven pattern (of saying), ‘I hate my in laws, they have done me wrong, I want to plan something’, it wasn’t as clear as that.”

Inside the Mind of the Mushroom Killer: A 7NEWS Spotlight special airs Sunday at 8.45pm