When soldier Kynan Watego Devenna returned to Australia from Afghanistan with post-traumatic stress disorder, he kept smelling rotten flesh and seeing dismembered bodies.
Three years after his return, the former rifleman burnt his ex-girlfriend's body after stabbing her twice in the neck.
The 32-year-old was sentenced on Friday to life in jail for the murder of Sarahjane Dower, the mother of his two children, in September, 2012.
The defence case during the four-day trial at the Townsville Supreme Court argued Devenna had gone into "army mode" while killing Ms Dower and had "disorganised thoughts" after the act.
He pleaded guilty to manslaughter on Monday but the Crown rejected the plea.
In handing down his sentence, Justice David North said Devenna demonstrated a "chilling cruelty" in a videotaped police interview in which he described Ms Dower's death.
"You're going to die," he told her after stabbing her once.
"I'm not going to call an ambulance."
He then watched her gasp for breath and stabbed her again because she was taking too long to bleed out. "That confession demonstrated that the murder of Sarahjane Dower was planned and premeditated," Justice North said.
Defence barrister Harvey Walters told the court Devenna suffered flashbacks that caused him to smell rotten flesh and see faces and dismembered bodies.
He had struggled to cope following the death of army mates in Afghanistan, had been admitted to hospital for self-harm and had suicidal thoughts and obsessive compulsive tendencies.
However, a psychologist believed he did not suffer a mental condition "that deprived him of the capacity to understand what he was doing".
Devenna had stopped taking medication before he met Ms Dower to talk about custody arrangements for their two children on the day of the murder.
He told police he had wanted her dead since 2007 when custody of their children first became an issue.
He was worried she was not taking them to school and that they would run away.
"In my mind she was never going to change and I was not going to stand by and watch my kids suffer," he told police after her badly incinerated body was found.
Justice North said Devenna had caused the children much suffering and grief.
"As a consequence of your crime, your children have lost their mother," he said.
"A loss that will be with them for the rest of their lives."
After the murder, Devenna cleaned the blood from his mother's Ayr home, drove Ms Dower's ute to High Range near Townsville and twice burnt it with her body inside.
Justice North said his actions to conceal the crime had placed his wife, Jody Marie Viero, and friend Jonathan Draper in the firing line of the law.
Viero pleaded guilty to attempting to pervert the course of justice and was given a three-year suspended sentence in April.
Mr Draper, who knew of the murder, gave Devenna money to buy diesel and picked him up from High Range.
Devenna will be eligible to apply for parole after 15 years.
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