There is no forensic evidence convicted serial killer Kathleen Folbigg’s four young children were smothered, according to lawyers who are petitioning for a judicial review of her case.

In 2003, Folbigg was found guilty of killing her two sons and two daughters over a 10-year period in the NSW Hunter Valley and was jailed for 40 years.

• Murderer predicts more prison riots
• Ravenhall: rioters burn golf cart, ride tractor
• Victoria Police quell prison riot

A NSW Supreme Court jury found Folbigg guilty of the manslaughter of her first baby, 20-day-old Caleb, and the murders of eight-month-old Patrick, 10-month-old Sarah and 18-month-old Laura.

She was also convicted of the grievous bodily harm of her second child Patrick when he was 4 months-old — over a smothering attack that left him blind.

The court heard Folbigg was unable to cope with the demands of motherhood and killed her children in fits of rage.

But in the petition made to NSW Governor General David Hurley, Monash University Professor of Forensic Pathology Stephen Cordner wrote, “If the convictions in this case are to stand, I want to clearly state there is no pathological or medical basis for concluding homicide”.

“It seems not to have been explicitly stated in the trial, but there is no forensic pathology evidence, no signs in or on the bodies to positively suggest that the Folbigg children were smothered or killed by any means.”

During the trial, the prosecution relied heavily on Folbigg’s diary entries about her children.

“Scared she’ll leave me now, like Sarah did,” she wrote of Laura in one entry.

“I knew I was short tempered and cruel sometimes to her and she left — with a bit of help”.

Clockwise from top left: Patrick, Laura, Caleb and Sarah Folbigg, who were killed by their mother Kathleen Folbigg.

“All I wanted her to do was shut up. And one day, she did,” she wrote about Sarah.

“Even though I’m responsible, it’s alright.

“She accepts and is happy. She’s a fairly good natured baby, thank goodness — it saved her from the fate of her siblings.

“I think she was warned … She saved her life by being different”.

She wrote, “Obviously I’m my father’s daughter,” in another entry.

Folbigg’s father Thomas Britton murdered her mother when Folbigg was a baby.

But a clinical psychologist for Folbigg’s legal team said the words were consistent with the thoughts and feelings of mothers whose children have died and maternal grief reactions.

As the ABC reported last year, lawyer Shaun McCarthy from the Newcastle Legal Centre has been working with a team of barristers and law students to prepare the petition for judicial review.

Folbigg’s friend, Helen Cummings told the ABC it was Folbigg’s mothering that was put on trial.

“She has gone through too much,” Ms Cummings said.

“She has lost four babies that she loved. There was no evidence to show she had smothered any of them.”

Ms Cummings compared Folbigg to Lindy Chamberlain.

“Lindy served two years and she shouldn’t have,” she said. “Kathleen is serving a lot more. Lindy was on trial because she didn’t cry at the right time.”

But Folbigg’s foster sister Lea Bown said the children would not rest in peace while the campaign to free her mother continued.

“I think it’s wrong,” Ms Bown said. “She was found guilty and she’s had two to three tries at trying to get out and have a new trial and it was knocked back.

“‘Somebody has got to speak up for the kids”.