A Perth father has been sentenced to life with a minimum of 31 years in jail for murdering his two young children to "punish" his wife after their marriage broke down.
Jason Craig Headland, 36, killed his three-year-old son Andreas and five-year-old daughter Zaraiyah-Lily at their home on Flight Vista in Yanchep on October 20 last year.
The court heard he drugged the children by crushing an antihistamine into their juice.
While a cause of death was not established, a pathologist found it was likely they died by asphyxiation after being drugged.
The Supreme Court was told that in the week leading up to the murders, Headland's wife — who is a fly-in, fly-out worker — ended their relationship and was staying with family while he was at the Yanchep home with their children.
The night of the murders he called Anatoria Headland to warn her.
"I'm going to hurt you ... I'm going to break your heart into 50 million pieces ... say goodbye to your kids. This is the last time you will speak to them," he told her.
Ms Headland called police who went to the property and discovered the bodies of the children, and Headland with self-inflicted stab wounds.
Beside him was a note claiming he had fought for the benefit of his family for too long and he had had enough.
In her victim impact statement that was read to the court, Ms Headland paid tribute to her "two peas in a pod", saying they were happy and bubbly children with so much love for each other and their family.
"You were supposed to be their protector … what you did was heartless and selfish," she said.
Justice Lindy Jenkins described Headland's behaviour as self-centred and vindictive, saying he used his children as "weapons" in disagreements with his wife.
"You made your children pay with their lives in order to inflict pain and loss on your wife. They had a right to believe you would protect and nurture them," she said.
She sentenced him to life in prison with a non-parole period of 31 years.
Headland's sentence will be backdated to October 2016.
