Kathleen Folbigg, convicted of killing her four children, gives an explosive explanation.

Warning: This post deals with the deaths of four young children.

Kathleen Folbigg became known as Australia’s worst female serial killer when in 2003 she was jailed for the murders and manslaughter of her four infant children.

Now, a new report is suggesting she may be innocent.

Behind the push to have Folbigg’s conviction for the deaths of her four children between 1989 and 1999 overturned is a forensic expert’s conclusion the babies died from natural causes.

It’s the subject of an Australian Story special that will air on Monday night on the ABC. In the program, Folbigg will explain for the first time what she really meant by the words she wrote in the diaries that played such a crucial role in her conviction.

The fate of Folbiggs’ four children

NSW couple Kathleen and Craig Folbigg had their first child, Caleb Gibson, on February 1, 1989. Just 19 days later, on February 20, Kathleen said she found her son dead in his cot, court documents say. His death was attributed to Sudden Infant Death Syndrome (SIDS).

In June 1990, their second child, Patrick Allen was born. One morning in October that year Craig said he awoke to sound of his wife screaming and rushed over to find her standing by his cot and the little boy unresponsive. Craig managed to revive his son until an ambulance arrived, taking him to hospital. Doctors couldn’t determine what had caused Patrick to stop breathing, but diagnosed him with epilepsy.

On February 13, 1991, Craig got a call from his wife at work. “It’s happened again,” she screamed. According to court documents the father arrived at the same time as paramedics and found his son lying unresponsive in his cot. Patrick was pronounced dead at hospital, with a doctor determining he had suffered cardiac arrest – though a later autopsy could not find what had caused this.

In October 1992 the couple’s third child, Sarah was born. In August 1993, Craig was again awoken by his wife’s screaming to find his child unresponsive on her bed. An autopsy found that Sarah had small cuts near her mouth and that injuries to her lungs were consistent with “asphyxiation caused by the application of mild force” – yet her death was determined to be caused by unknown natural causes, SIDS.

Laura was born in August 1997 and made it to March 1, 1999, before her sudden death while her mum was alone with her around lunchtime. Doctors found that the 19-month-old had suffered with myocarditis, inflammation of the heart muscle, but did not determine it to be the cause of her death.

In 2003, Kathleen, then 35, was found guilty of Patrick, Laura and Sarah’s murder, and Caleb’s manslaughter. Kathleen was the first at the scene in all four cases.

Explaining her dairies

These four deaths were attributed to tragic acts of God – until the day Craig found his then-estranged wife’s diaries.

The words in those diaries, and another uncovered by police, painted a damning picture of Kathleen’s guilt, and led to her 2003 conviction and sentencing to 40 years jail, 30 years non-parole, which was later reduced to 25 years on appeal.

In one diary entry, Kathleen wrote of Laura, “She’s a fairly good-natured baby. Thank goodness. It has saved her from the fate of her siblings. I think she was warned.”

In another entry: “I feel like the worst mother on this Earth. Scared she’ll leave me now like Sarah did. I knew I was short-tempered and cruel sometimes to her, and she left. With a bit of help.”

At another point, she also referenced her father, who had killed her mother 1969: “I am my father’s daughter.”

Kathleen explained to Australian Story that her diaries were written "from a point of me always blaming myself".

"I blamed myself for everything. It's just I took so much of the responsibility, because that's, as mothers, what you do."

The prisoner also explained the quote: "She left. With a bit of help" referenced "God or some higher power".

New report says the deaths were from "natural causes"

Folbigg's lawyers commissioned a report from Professor Stephen Cordner, after he examined the medical evidence presented at the trial.

Professor Cordner concluded in the 2013 report that there was no evidence, or as he puts it "positive forensic pathology support" for the idea the children had been killed.

He contended instead that the children each died of natural causes, Sarah and Caleb to SIDS, Patrick to a complication relating to his epilepsy, and Laura to myocarditis. Another expert who Australian Story spoke to, agreed with this conclusion, which goes against the jury's findings.

With this report, Kathleen's legal team are seeking a judicial review of the case and have petitioned the Governor of NSW.

You can watch 'From Behind Bars' on Australian Story at 8pm Monday on ABCTV and ABC iview.