Australia's 'worst female serial killer' Kathleen Folbigg released after help from Spanish scientist

An Australian woman who spent 20 years in prison for killing her four children was pardoned and released on Monday following an inquest into her guilt.

Kathleen Folbigg, now 55, was dubbed "Australia's worst serial killer" after being convicted in 2003 of murdering three of her children, and convicted of manslaughter in the death of the fourth. 

According to prosecutors, her children, aged between nine weeks and three years, had been suffocated to death by Folbigg, who has always rejected these accusations, claiming that each of their deaths was linked to a natural cause.

A pardon on the grounds of reasonable doubt was seen as the quickest way to secure her release from prison -- a subsequent inquiry could see her convictions quashed completely. 

Kathleen Folbigg spent her two decades in prison being demonised. 

Once the most reviled name in Australia, Folbigg has been cleared thanks in part to a Spanish scientist Carola García Vinuesa, who, along with other colleagues, has managed to show the children could have died of natural causes.

"The theory that she had killed her children had no evidence. The only evidence was circumstantial, because she was the one finding them dead," García Vinuesa told Euronews.

"Folbigg is very grateful, not only to us - the scientists - but also to her lawyers, who have done most of the work for free," she adds.

The first to die was her son Caleb, aged 19 days. One night, Kathleen woke up because she needed to go to the toilet. She checked on her baby and realised he wasn't breathing.

"There's something wrong with my baby," she shrieked. Her husband came running, and they tried to resuscitate the child, but by the time the ambulance arrived he was dead.

After this she lost Patrick when the baby was