A Tasmanian man who allegedly attempted to murder his estranged wife and two young sons with a box cutter had previously told his wife he understood why fathers killed their children, a jury has heard.
WARNING: This story contains graphic details that readers may find disturbing.
Damian Leslie Harper has pleaded not guilty to three counts of attempted murder, one count of wounding, and aggravated burglary.
It is alleged the 47-year-old travelled from his Hobart residence in the state's south to his in-law's home in the north-west — about a 300km trip — where his wife and sons were staying, in January 2019.
He allegedly broke into the Cuprona home in the early hours of the morning through a partially opened kitchen window and entered the bedroom where his sons were sleeping.
He then cut his four-year-old son with a stanley knife, before reaching for his six-year-old son on the upper level of the bunk bed they were sleeping in, a jury heard.
Giving evidence on Friday, the mother told the Burnie Supreme Court she woke up to her sons' screams and raced out of bed to find the accused bending over the bottom bunk.
"I saw Damian had a knife and there was blood on the bed," she said.
The woman said she tried to pull her sons away from Mr Harper, but he pushed her up against the wall, stabbed at her and said, "I'm going to kill you, you f**king b***h."
"I was trying to fend him off, I was screaming," she said.
The woman said she called out to her father, who "came in with all his might" and pushed the accused into the corner.
The DPP alleged the accused slashed at the father-in-law during the altercation.
Harper was 'controlling and manipulative', wife says
On Thursday, Defence lawyer Greg Richardson said he did not contest that Mr Harper entered the home wielding a weapon, but said the trial must consider his intentions at the time.
"Virtually all the factual assertions will not be challenged. This trial is all about the mental elements, about what his state of mind was, what his capacities were," he said.
"The primary issue is, what on earth was going on in his mind?"
The children's mother told court on Friday that Mr Harper had previously told her while watching media reports that "I understand why fathers kill their children".
"He said that their mothers pushed the fathers into it, pushed them too far," she said.
The court heard Mr Harper had become "controlling and manipulative" after their first few years together, but their marriage began to unravel after January 2018, when his wife went on a work trip.
On returning from the trip, the jury heard a male colleague who she had travelled with told Mr Harper he could "have her back now".
The woman said Mr Harper's mental health had continued to deteriorate from that point.
The jury heard shortly after a doctor indicated Mr Harper had a delusional disorder.
It heard Mr Harper was hospitalised on a mental order for a week in March and then continued to insist his wife take a lie detector test to prove infidelity — an accusation she was "extremely upset by".
"He became much more controlling and accused me of having affairs," she said.
"I would say how hurt I was that he would think I'd done that, because I didn't.
"He became much more verbally aggressive."
She said Mr Harper would take her phone away from her and would show up at her workplace unannounced.
"He became very volatile and angry," she said.
The court heard the couple separated in May 2018, and the woman took out a Police Family Violence Order against him.
She said between leaving, apart from contact with lawyers and the courts, the accused had no contact with herself or their children.
