Sydney, Jun 5 (IANS): After spending 20 years in jail, a woman once called Australias "worst female serial killer" was pardoned on Monday after new evidence suggested that she did not kill her four infants.

New South Wales Attorney General Michael Daley intervened to order Kathleen Folbigg be freed, based on the preliminary findings of an inquiry that had found "reasonable doubt" as to her guilt for all four deaths, reports CNN.

Addressing reporters on Monday, Daley said that he had spoken to the governor and recommended an unconditional pardon, which had been granted.

"This has been a terrible ordeal for everyone concerned and I hope that our actions today can put some closure on this 20-year-old matter," Daley said.

The 55-year-old's case has been described as one of Australia's greatest miscarriages of justice.

Folbigg was jailed in 2003 on three counts of murder and one of manslaughter following the deaths of her four children -- Caleb, Patrick, Sarah and Laura -- over a decade from 1989.

In each case, she was the person who found their bodies, though there was no physical evidence that she had caused their deaths.

Folbigg has always maintained her innocence, the BBC reported.

Each child died suddenly between 1989 and 1999, aged between 19 days and 19 months, with prosecutors at her trial alleging she had smothered them.

Previous appeals and a separate 2019 inquiry into the case found no grounds for reasonable doubt, and gave greater weight to circumstantial evidence in Folbigg's original trial.

But at a fresh inquiry, headed by retired judge Tom Bathurst, prosecutors accepted that research on gene mutations had changed their understanding of the children's deaths.

The pardon comes after a years-long campaign to free Folbigg, sparked when a team of immunologists found her daughters shared a genetic mutation that can cause sudden cardiac death.

Evidence was also uncovered that her sons possessed a different genetic mutation, linked to sudden-onset epilepsy in mice.