In the Tasmanian Supreme Court on Thursday, Justice Tamara Jago sentenced Kerry Lee Whiting, 47, for the murder of Adrian Mayne and the attempted murder of Natalie Harris, at their home in the Launceston suburb of Ravenswood, on November 25, 2021.
Imposing a jail term of 38 years, with a non-parole period of 24 years, Justice Jago told Whiting the crimes were the result of his "controlling, possessive and jealous attitude".
"You were not willing to allow her to move on in her life and you resented the presence of Mr Mayne in your children's lives, so you determined to kill them," Justice Jago said.
Kerry Lee Whiting was arrested a week after murdering his ex's new partner and trying to kill her. (HANDOUT/TASMANIA POLICE)
"Tragically, you achieved that in respect to Mr Mayne, but your plan was thwarted in respect to Ms Harris by the brave and desperate actions of (her 16-year-old son) T, who was awoken by the screaming and intervened, dragging you away from his mother.
"That, and the first aid he later provided to his mother, undoubtedly, in my view, saved her life."
Whiting had been abusive and violent during their 20-year relationship, which ended in June 2021, Justice Jago said.
After moving out, Ms Harris met Mr Mayne online, and they had been living together for four months with two of the children she shared with Whiting, T and K, then aged 16 and 14.
In the weeks leading up to the crime, Whiting made threats to injure or kill Mr Mayne, which were heard by the children.
Justice Jago said Whiting rode a bike to the couple's home and entered it in the early hours of November 25 going to their bedroom with a kitchen knife.
"You immediately started stabbing Mr Mayne. You launched an attack on a vulnerable and defenceless person," she said.
Mr Mayne tried to protect Ms Harris, throwing himself over her boy and yelling "don't stab her", she said.
"She got out of the bed and you continued stabbing her. At one point when you were attacking Ms Harris, she said to you 'why are you doing this?' You responded by saying 'you caused this'.
Her screams woke the children, and T rushed to protect his mother.
"Even after his intervention, you continued to stab Ms Harris," Justice Jago said.
"T pushed you up against a wall and challenged you. He said he would grab the knife and hurt himself if you did not drop it. He said to you 'you're my Dad, why are you doing this … I don't ever want to see you again.' You replied 'oh, it's not like you message me anyway'."
The judge said this evidence indicated Whiting's callous arrogance and controlling nature.
"It is difficult to envisage a more arrogant and cold-hearted act," she said.
Mr Mayne was fatally stabbed 20 times and Ms Harris was stabbed 27 times. She suffered life threatening injuries and was in intensive care for six days.
Whiting fled the home and was arrested a week later.
Justice Jago said family violence was an insidious problem that demanded condemnation.
"There is a clear need for the denunciation of violent manifestations of possessive, controlling and jealous behaviours following the breakdown of relationships," she said.
"There can be no tolerance for men who seek to extend their want for control over relationships in such an extreme and tragic manner."
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