• Mourners attend a floral tribute near a house in which eight children were killed in the Cairns suburb of Manoora. (AAP)Source: AAP
A mother who killed eight children will never stand trial after a Queensland court ruled she was of unsound mind at the time.
4 May 2017 - 9:40 AM  UPDATED 4 May 2017 - 1:57 PM

A Cairns mother who killed her seven children and a niece thought she was saving them from the end of the world.

She was smoking up to 20 cones of cannabis a day when she developed a severe form of schizophrenia in late 2014.

The 37-year-old believed she was the "Chosen One" and became obsessed with cleansing to protect her and her family from demons.

On December 19, about a month after the religious delusions began, she heard a "dove call" telling her it was time to act.

The doting mother first killed the family's pet duck, then turned on the children - four boys and four girls, aged between two and 14 years.

Quickly realising what she had done, she attempted to take her own life and waited to die on the front verandah where she was found by her adult son, who called triple zero.

She was charged with eight counts of murder but will never stand trial after the Mental Health Court last month found she was of "unsound mind" at the time of the killing.

Justice Jean Dalton said there was a convincing body of evidence that the mother suffered a psychotic episode and had no capacity to control or understand her own actions.

"To her way of thinking at that time what she was doing was the best thing she could do for her children, she was trying to save them," Justice Dalton said.

The court heard the woman remained in a state of psychosis until July 2015 despite attempts to alleviate her symptoms with several different anti-psychotic medications.

She has since relapsed twice, once at the two-year anniversary of the killings, and expressed the desire to kill other patients in the high-security facility where she is being held.

Psychiatrist Frank Varghese said the woman's illness was "schizophrenia at its very depth and at its worst".

"This is quite a unique case and a horrendous case, the likes of which I've never seen before," Dr Varghese told the court.

Several psychiatrists agreed the mother's persistent and lifelong abuse of cannabis triggered her schizophrenia, despite the illness usually manifesting in the younger years of life.

The woman did give up drugs and alcohol as part of her obsession with cleansing but by then it was too late, the symptoms had acquired "a life of their own".

The court heard she had no criminal history and had not been in contact with psychiatric services despite previous disturbing episodes.

Justice Dalton ordered the woman continue to receive involuntary treatment and be allowed escorted leave on the hospital's grounds.

She said she was impressed that the mother had acknowledged what she'd done and appreciated her rehabilitation was being hindered by grief and post-traumatic stress disorder.

"Her children were the things that had given her the most happiness in life," Justice Dalton said.

The Mental Health Act prohibited Justice Dalton's decision, made on April 6, from being published for 28 days.

Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.

Suicide Call Back Service 1300 659 467.

Multicultural Mental Health Australia www.mmha.org.au.

National domestic violence helpline: 1800 737 732 or 1800RESPECT. In an emergency call triple zero.