The youth, who was aged 17 at the time of the alleged offences, on Monday in the Brisbane Supreme Court pleaded not guilty to the murder of Emma Lovell at her North Lakes home, north of Brisbane, after midnight on December 27, 2022.
The youth also pleaded not guilty to armed break-in as well as malicious acts and assault occasioning bodily harm towards Ms Lovell's husband Lee, who was kicked and then stabbed in the back.
Lee Lovell was kicked and then stabbed in the back. (Jono Searle/AAP PHOTOS)
The youth was recently granted an application for a judge-only trial due to youth crime being a central issue ahead of Saturday's Queensland election and previous media reports that made claims about his criminal record.
Crown prosecutor David Nardone told Justice Michael Copley on the first day of the trial on Monday that the youth had not directly carried out the violence against Emma and Lee Lovell.
"The primary liability of the accused is through the common purpose, by the time it was put into execution, to steal while armed with a knife," Mr Nardone said.
"The acts of the co-offender were likely to endanger human life."
Mr Nardone said the youth was guilty of the acts committed by the other 17-year-old as the probable consequences of their shared actions to break into a home while armed with a knife.
The other teen charged over Ms Lovell's death pleaded guilty in March to her murder and in May was sentenced to 14 years' imprisonment.
Mr Nardone said the defendant attended youth accommodation about 120 metres from the Lovells' home on December 26, 2022 before his companion likely took a knife from that location and the pair walked down the street at 11.30pm.
Justice Copley was told security camera vision from the Lovells' home would be crucial to the case and he would see the co-offender test the front door and find it unlocked before the defendant entered.
"The co-offender moves his hand in front of the accused's face. It is a matter of centimetres between the knife and his face," Mr Nardone said.
The prosecutor said the Lovells were woken by their dogs and found the two youths in their home, leading to a confrontation that moved to the front door.
Ms Lovell was fatally stabbed once through the heart on the front lawn.
Her husband was stabbed and then kicked while he was on the ground.
Mr Nardone said the defendant's black hat was found on the Lovells' front lawn and he was tracked by police dogs to the youth residence where he and the co-offender were located and arrested.
Defence barrister Laura Reece said the prosecution would have to prove beyond reasonable doubt that the youth knew the other teen had a knife prior to the home invasion.
The trial is due to run for another four days.
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