Two decades ago, Kathleen Folbigg was convicted of smothering all four of her young children. Australian tabloids called her the country’s worst female serial killer.
But Ms. Folbigg, who was serving a 30-year term, insisted she was innocent. And in recent years, a growing number of scientists began to argue that she was telling the truth. Genetic evidence, they said, indicated that the children had very likely died of natural causes.
On Monday, the attorney general of New South Wales, Michael Daley, announced that Ms. Folbigg, 55, had been given a full pardon and released from prison. He cited an official inquiry’s preliminary conclusion that there was “reasonable doubt” about her guilt.
“What is the difference between today and what has transpired in the past is that new evidence has come to light,” Mr. Daley said. “It is appropriate that we do have the mechanisms to reconsider the source of questions in light of new evidence.”
The Australian Academy of Science, which acted as an independent adviser to the investigation, described the case as “Australia’s greatest miscarriage of justice” and said the outcome showed that the inquiry had “comprehensively listened to the science.”
Mark O’Callaghan, one of Ms. Folbigg’s lawyers, said that her legal team was “grateful to see Kathleen Folbigg released this morning.”
The former New South Wales chief justice who led the official inquiry, Tom Bathurst, said in a statement on Monday that he was unable to accept “the proposition that Ms. Folbigg was anything but a caring mother for her children.”
He said he had concluded that there was a reasonable probability that three of the four children had died of natural causes, and that prosecutors’ argument that she’d killed the fourth had relied on “coincidence and tendency evidence” that no longer held up.
All four of Ms. Folbigg’s children died before the age of 2: Caleb, at 19 days, in 1989; Patrick, at 8 months, nearly two years later; Sarah, at 10 months, in 1993; and Laura, at 18 months, in 1999.
Initially, the deaths appeared to be simply a series of horrific tragedies. Two were deemed to have been from sudden infant death syndrome, a third from choking. A coroner concluded that Laura had died from an “undetermined” cause.
But after Ms. Folbigg’s husband found one of her diary entries, which said that Sarah had left the world “with a bit of help,” he turned her in to the police.
There was no direct evidence that Ms. Folbigg had smothered the children, as prosecutors alleged. She told the authorities that her diary entries had reflected the stress of motherhood, and that “a bit of help” referred to her hope that God had taken her baby home.
But at her 2003 trial, the prosecutors argued that it was more likely that pigs would fly than that four young children would die of natural causes so young, in the same family, over a span of 10 years. A jury agreed, and Ms. Folbigg, then 35, was found guilty of murder in the deaths of Patrick, Sarah and Laura, and of manslaughter in Caleb’s.
But in recent years, geneticists have found that Ms. Folbigg and her two daughters had a rare genetic mutation in what is known as the CALM2 gene. In 2020, an international team of scientists published a research paper concluding that the mutation was likely to result in life-threatening cardiac arrhythmias. Further research found that the two boys had separate rare genetic variations, which in mice have been linked to lethal epileptic seizures.
Since scientists began raising questions about the case, two official inquiries have been conducted. The first, in 2018, focused on her diary entries and found that there was no reasonable doubt about Ms. Folbigg’s guilt.
The second inquiry, led by Justice Bathurst, began last year, after more than 90 prominent scientists, including two Nobel laureates, submitted a petition to the governor calling for Ms. Folbigg’s immediate release. Besides examining the genetic research, this inquiry heard evidence from psychiatric experts who said Ms. Folbigg’s diary entries did not contain a clear admission of guilt.
Anna-Maria Arabia, the chief executive of the Australian Academy of Science, said at a news conference on Monday that scientific evidence had been “critical” to the case and that leading scientists from around the world had aided the inquiry.
But Australia’s legal system needs to ensure that every case, not just “exceptional” ones, have access to such assistance, she added. “We need ways, particularly when all the appeals mechanisms have been exhausted — as was the case for Kathleen Folbigg — for that science to be heard,” she said.
Mr. Daley, the attorney general, said that Justice Bathurst would decide whether to refer the case to the Court of Criminal Appeal for Ms. Folbigg’s conviction to be overturned. If that happens, Ms. Folbigg could sue the state of New South Wales for compensation, he said.
He declined to comment on Ms. Folbigg’s guilt or innocence, but said: “We’ve got four little bubbas who are dead. We have a husband and wife who lost each other, a woman who spent 20 years in jail and a family that never had a chance. You’d not be human if you didn’t feel something about that.”