Carol Matthey was cleared of murdering her kids. Now, she's defending killer Kathleen Folbigg.

She’s known as “Australia’s worst female serial killer”, but according to Geelong mum Carol Matthey, baby murderer Kathleen Folbigg could be innocent.

Matthey, who was herself cleared for the murders of her own four children after they died unexpectedly between 1998 and 2003, has claimed her case could prove Kathleen Folbigg’s innocence, stating “medical experts” could be wrong about the causes of death for Folbigg’s four children.

In her first ever interview, with Tara Brown on 60 Minutes, Matthey speaks of the deaths of her babies – Jacob, Chloe, Joshua and Shania – who all died in her care, but not all from Sudden Infant Death Syndrome as Folbigg has claimed in her case.

Kathleen Folbigg is Australia’s worst female serial killer, convicted of killing her four babies. 8.30 TONIGHT: Tara Brown uncovers an identical tragedy: four children dead, but this time the mother walked free. What really happened? A #60Mins that will divide the country. pic.twitter.com/VFuEUYsyu3

— 60 Minutes Australia (@60Mins) March 17, 2019

In 1998, Jacob passed away aged seven months. Two years later, Chloe died at nine weeks. Both suffered Sudden Infant Death Syndrome, known as SIDS.

But a further two years down the line, three-month-old Joshua suddenly stopped breathing. His death was attributed to a blood infection by doctors, leaving Matthey distraught.

It was the fourth death, of her three-and-a-half year old daughter Shania in 2003, which raised suspicions, ultimately launching an investigation into all four children’s deaths.

As Shania was too old for SIDS, medical experts couldn’t explain her sudden passing.

In court, Matthey said her child fell from a coffee table, started screaming and stopped breathing, prompting a call to an ambulance. She died the next day after Matthey declined an offer by paramedics to take the child to hospital.

The explainable death led to Matthey’s arrest and charge in 2005 for the horrific act of murdering all four children, leaving one remaining son, now 21.

She maintained her innocence, and in 2007, the case was dropped following star witnesses’ evidence being thrown out of court.

As reported by the Herald Sun, Justice John Coldrey ruled a large amount of the medical evidence inadmissible.

“What is abundantly clear from an overview of the medical evidence is the conflict in expert opinion as to the cause of death of each of the Matthey children,” Justice Coldrey said.

The overturned case bears striking similarities to notorious killer Kathleen Folbigg, who claimed her four babies died from SIDS between 1989 and 1998.

She was later charged with the murder of three of the children and the manslaughter of a fourth, and is currently serving a 30-year sentence.

Much like Mattey, Folbigg has always maintained her innocence.

In his ruling of the Matthey case, Justice Coldrey had looked to precedents set by the case of Kathleen Folbigg, adding that "medical evidence in these types of cases was unique and presented a challenge for the courts", according to the Herald Sun.

With an inquiry into her conviction approaching, Folbigg could soon walk free after 15 years behind bars.

Matthey strongly believes this could be the outcome. She believes her family's tragedy is proof that the deaths of Folbigg's babies could merely be a medical mystery, not a disturbing crime.

"Medical experts can be wrong and are wrong," she said.

"She could be innocent."