Australian mother Kathleen Folbigg pardoned, released from jail after 20 years

A mother who was once called Australia's worst serial killer has walked free from prison. 

Kathleen Folbigg spent two decades behind bars over the deaths of her four children, but she has been pardoned after experts testified they died of natural causes.

When Folbigg's four children died, it changed her life. Twenty-five years later, six words from New South Wales' Attorney-General Michael Daley changed it once more: "Ms Folbigg has now been pardoned."

Folbigg was freed from prison immediately.

"She will not have to serve the rest of her sentence," Daley said.

It ends a 25-year wait for justice. The mother was convicted in 2003 of killing all four of her children who died suddenly. Caleb died aged just 19 days old, Patrick was eight months, Sarah was 10 months, and Laura was one-and-a-half years old.

She argued it was natural causes, but diary entries about how she was responsible for her children "leaving" her were treated as an admission of guilt and she was convicted.

"There has never been any forensic or pathological evidence to say the children were smothered," said NSW MP Sue Higginson.

It was always believed Caleb died of sudden infant death syndrome. In the case of the others, new science examined old evidence recently revealing that Folbigg and her two girls shared a rare genetic mutation that could silently kill. 

They can't determine if it did kill her children, but they can't say it didn't. 

"There is reasonable doubt as to the guilt of Ms Folbigg for each of those offences," Daley said.

Monday's events brought Folbigg's fight to clear her name to an end. 

"It's been a 20-year-long ordeal for her," Daley said. "We wish her well for the rest of her life."