A man accused of fatally bashing and stabbing his pregnant partner at their home in Sydney's west does not deny he caused her death but says he was "mentally ill" at the time, a court has heard.
Joshua Scott Homann allegedly stabbed 37-year-old Kirralee Paepaerei, his de facto partner of two years, almost 50 times in the neck and chest late on September 21, 2015, in the bedroom of the Mount Druitt home they shared.
Kirralee Paepaerei was pregnant when she was stabbed to death in September 2015.
He then fled their two-storey townhouse by jumping out of a window and drove to the nearby police station, where he claimed he had been attacked during a home invasion.
Two young relatives of Ms Paepaerei, who had been in the home and heard the sound of glass smashing, went upstairs and called triple zero after they found the body of the mother-of-four.
At the opening of Mr Homann's murder trial on Wednesday, Crown prosecutor Sean Hughes said a heavily breathing and stuttering Mr Homann walked into Mount Druitt police station six minutes after fleeing the house, wearing no shirt and no shoes.
Officers inside the station noticed a small amount of blood on his head before Mr Hughes said Mr Homann leaned over the front counter and shouted: "We need to get someone to Chester Street, someone broke into my house and tried to stab me."
Joshua Scott Homann has been charged with his partner's murder.
Mr Homann then said his partner was home, the trial heard, and said, "We need to make sure she's OK."
Officers said they would get an ambulance to the house, asking what happened.
"Someone came into my house and tried to kill me," Mr Homann told police, according to Mr Hughes. "I jumped out the window and drove straight here."
Mr Hughes told the jury of nine men and three women the claim of driving straight to the police station was "a lie", because later tests by police found the distance could be covered in two minutes if a driver was moving at the speed limit and had stopped for a red light.
"If indeed that was true, if someone had broken in, he would have driven straight there," Mr Hughes said.
"The evidence suggests he couldn't have. Claims to the police at that time, of the intruder in the home, were false and a lie.
"There was no such intruder. The deceased died at the hand of the accused, and the accused alone."
An ambulance was called at 12.06am on September 22, arriving at the home on Chester Street a short time later.
Paramedics were unable to revive Ms Paepaerei or save her unborn child.
Mr Hughes said a bloodied 15-centimetre knife was found on the mattress in the bedroom along with a metal rod. Both implements were covered in the blood of Ms Paepaerei and Mr Homann.
He said blood was also on the walls of the bedroom, showing the "sustained" nature of the attack. Some of the blood was diluted, suggesting someone had tried to wash it away.
The court heard Ms Paepaerei suffered "extensive blunt force injuries" to her face and abdomen, 28 incision or stab wounds on her neck, and 21 stab wounds to her chest.
DNA testing performed at an autopsy showed Mr Homann was the father of the unborn child.
Mr Homann's barrister Peter Lange said his client, who was found with methamphetamine in his system, "will not be suggesting he's not responsible or did not cause the death of Ms Paepaerei".
"What is the issue is what was going on in the mind of Mr Homann that night," Mr Lange said.
He said his client had been exhibiting "erratic behaviour" about the time of the attack, and the trial would hear evidence from psychiatrists of other incidents involving Mr Homann.
"Ultimately I'll be suggesting, members of the jury, this is not a case about domestic violence," Mr Lange said. "This is not a case about drug use. What this case is ultimately about is the power of mental illness.
"I'll ask you to keep an open mind, listen to the evidence, and focus on what is going on in the mind of Mr Homann that night."
The trial continues.