“It’s over. The Attorney-General should get on with it. There is evidence as to natural causes of death and it’s strong, and there is no evidence of suffocation of any of her babies,” said Dr Cavanagh, one of a number of Hunter lawyers working with a University of Newcastle Legal Centre team since 2013 on the Folbigg review case.

“You can’t have a conviction where there’s a natural cause of death and yet that’s what’s occurred here and she’s been in jail for 15 years because of it.

“They should get her released and then have an inquiry which should focus on the real issues of how a miscarriage of justice occurred.”

There is renewed focus on the deaths of the Folbigg babies Caleb, Patrick, Sarah and Laura between 1989 and 1999 after tapes of Folbigg speaking from Cessnock jail were played on Australian Story on Monday night.

Former NSW Director of Public Prosecutions Nicholas Cowdery told the program he believed the jury got it right when it convicted Folbigg, but he agreed with Dr Cavanagh that three years was too long to wait for a decision from the Attorney-General after Folbigg’ petition for a judicial review was lodged in June, 2015.

The petition includes a 120-page report by internationally-respected forensic pathologist Professor Stephen Cordner which criticised medical evidence given at the Folbigg trial.

He found much of the forensic pathology discussed at the trial was “misconceived” and the default diagnosis of murder was “wrong” because there was no forensic pathology support for the Crown case that Folbigg smothered her children.  

“There is no forensic pathology support for the contention that any or all of these children have been killed. If the convictions in this case are to stand, I want to clearly state there is no pathological or medical basis for concluding homicide," Professor Cordner said.

The Folbigg petition also raises questions about evidence given by at least two medical experts at her trial, after a Victorian Supreme Court judge questioned the “factual foundation” of their opinions in a 2005 case where Victorian woman Carol Matthey was charged with murdering her four babies.

Victorian prosecutors withdrew the murder charges against Mrs Matthey in 2007 after Justice John Coldrey said challenges to the evidence of pathologist Alan Cala and paediatrician/epidemiologist Susan Beal – who both gave evidence at the Folbigg trial two years earlier – required a “reconsideration of the cogency of their evidence”.

Both doctors were called by the prosecution to give evidence in the Matthey case after four medical experts said the four Matthey babies died of natural causes. 

Dr Beal told the Folbigg trial there was no natural cause for the Folbigg babies’ deaths and she was unaware of any case where three or more children in one family had died of natural deaths similar to the Folbigg case.

In a hearing before Justice Coldrey two years later in the Matthey baby deaths, Dr Beal said “all the evidence points to all the children having been killed by non-accidental suffocation”. 

Dr Cala also gave evidence in both the Folbigg and Matthey cases that the children died of smothering.

But Professor Cordner, one of the four medical experts who said there was no evidence the Matthey babies died of anything but natural causes, said it was “not for a pathologist to conclude that a number of infant or childhood deaths, with no significant pathological findings at all, are homicides on the basis of controversial circumstantial grounds”.

“If this case is to result in a prosecution, I want to clearly state there is no pathological basis for concluding homicide. The findings are perfectly compatible with natural causes,” Professor Cordner concluded in the Matthey case two years after Folbigg was convicted, and a decade before he would reach a similar conclusion in a report on the Folbigg babies’ deaths.

“The very existence of the enigma of Sudden Infant Death Syndrome demonstrates how little we know about why some babies die,” Professor Cordner said in the Matthey case.

In his decision that led to charges against Mrs Matthey being dropped, Justice Cordley noted that questions about the Folbigg case were raised in the Australian Journal of Forensic Sciences by 2007 in an article titled “The Case of Kathleen Folbigg: How did justice and medicine fare?”

The University of NSW School of Psychology authors examined medical evidence at the Folbigg trial and found “the case lays bare the inherent uncertainty and fallibility of medical opinion about the cause of an infant’s sudden and unexpected death”.

“The case illustrates how developing a legal argument that the accused has committed the crimes can transform circumstantial evidence, which may have been unrelated or innocent, into markers or ‘proof’ of guilt,” the authors Sharmila Betts and Jane Goodman-Delahunty found.

“Numerous inferences were drawn to fit circumstantial evidence into a compelling argument to find the accused guilty. Inferences are as prone to error as professional judgment. Whether existing legal procedures can effectively minimise these errors is a separate issue.”

While the Folbigg jury was told by the judge in the summing up in the 2003 trial that there was “no authenticated record of three or more such deaths in a single family”, the Folbigg petition cites a number of such cases around the world by the time of the Folbigg trial. 

In 2007 Justice Cordley challenged the medical evidence and noted: “The rarity of the phenomenon of four unexpected and seemingly unexplained deaths in one family cannot, of itself, provide a cause of death.”

In a statement last week Mr Speakman said the Folbigg petition “raises complex questions to which I am giving appropriate consideration and have taken extensive advice”.

“I hope to be in a position to make an announcement in the near future,” he said.