A 43-year-old Australian woman has been sentenced to 20 years in jail for gassing to death two of her children and attempting to kill another, back in 2002.
The woman, who cannot be named, was last week found guilty of two counts of murder and one of attempted murder.
The Brisbane Supreme Court was told that she gassed her eight-year-old son and 10-year-old daughter at her Sandstone Point home, near Bribie Island, and tried to kill her then 16-year-old son.
At the time of the killings she had been angry that her ex-husband had won a Family Court order to have the children for the first half of the 2002-2003 school holidays, which included Christmas.
She sobbed as Justice Philip McMurdo described her actions as "horrible".
"The prime motivation was to avenge what you regarded as the wrong done to you by your ex-husband, the children's father," he said.
During a two-week-long trial the jury heard that in November 2002 the woman crushed sedatives in her children's milk before telling them they were "going for a drive".
As the car was parked in the garage of their rented home, she attached a hose from the exhaust pipe to the car's open window and ran the engine.
The act was a bid to take her own life as well as her son aged eight, a daughter aged 10 and her severely physically and intellectually disabled son, aged 16, the court heard.
As the younger children were being gassed to death by the car fumes, the eldest boy and the woman escaped the garage.
Almost two days later the decomposing bodies of the two younger children were discovered by a neighbour.
The woman and the teenage boy were found inside the house.
The jury was told the woman had asked people how to die from carbon monoxide fumes.
Pathologist Dr Guy Lampe, who performed the autopsies, said the children's bodies showed classic signs of carbon monoxide poisoning.
Dr Lampe said the skin and organs of the children all displayed "cherry-pink discolouration", and that there were also traces of sleeping pills in their systems.
He said it could take as little as 20 minutes for a child to die from carbon monoxide poisoning.
''If gases can't escape easily, the level of carbon monoxide increases ultimately to be fatal to those within the space,'' he said.
After the children's death she admitted to other prison inmates she planned to escape being found guilty of murder by saying she had mental problems which stemmed from cannabis use, prosecutors alleged.
She had left a suicide note, asking her mother to look after her pet bird.
In her evidence to the jury, the woman testified a thought of taking herself and her children "to a better place" came over her on the day of the killings.
"My head appeared to order me to do it," she said.
"That order took over my mind."
However the jury rejected the woman's defence arguments that she had been of unsound mind and did not know what she was doing was wrong.
At Wednesday afternoon's sentencing hearing Crown prosecutor Simone Bain said the woman's actions were "unthinkable".
She said the surviving child had been robbed of the "love and companionship" of his two siblings.
"These were selfish crimes committed out of hatred and anger for the former husband," she said.
In handing down his sentence, Justice McMurdo said the woman knew what she was doing and held dispute over custody could not excuse the taking of two young lives.
"On no rational view could this begin to justify an attack on the children, let alone the killing of them."
The woman, who has already served 560 days in pre-sentence custody, will be eligible for parole after serving 20 years.