Security footage has been played in the Perth children's court of the moment a teenager threw a lump of concrete through a car window, fatally injuring a pregnant woman.
Members of Diane Miller's family cried in the public gallery as the CCTV footage was shown at the sentencing hearing for the 17-year-old, who has pleaded guilty to unlawfully killing the 30-year-old mother.
Ms Miller died in hospital three days after she suffered a catastrophic injury when she was hit in the head by the concrete as she sat in the front passenger seat of a car that was driving away from a shopping centre car park in Karawara in November last year.
Her young son Lloyde was in the back seat at the time.
It followed an altercation that had started when Ms Miller's partner believed a group of youths, including the teenager, had thrown something at his car.
The court heard a melee followed in the car park and some of the youths armed themselves with weapons, including pieces of concrete and stools.
Attempts made to defuse situation, court hears
The court heard some members of Ms Miller's group tried to defuse the situation and were yelling for the youths to stop, saying her baby was in the car and that she was pregnant.
After a few minutes, the altercation began to de-escalate but prosecutor Clare Cullen said as Ms Miller's car drove away the teenager, who was standing behind a wall, threw the concrete.
It was later seized by police and found to weigh 1.9 kilograms, measuring 225mm x 160mm x 50mm.
At the start of proceedings, Children's Court President Hylton Quail expressed his condolences to Ms Miller's family, including her brother, sister and mother.
Judge Quail said he intended only to hear submissions from the prosecution and defence lawyers on Thursday, and then proceed to sentencing the teenager on Friday.
Teen threw rock 'without thinking': defence lawyer
Defence lawyer Kate Turtley-Chappel said during the melee, her client had feared for his safety and the safety of others.
She said while the altercation had de-escalated by the time he threw the concrete and had walked away from the scene, he had various deficits, which meant he was unable moderate his behaviour.
Ms Turtley-Chappel said his intention had only been to
break a window or hit the car, and he had picked up the concrete and thrown it "without consequence".
"He threw a rock without thinking and ultimately it ended in the loss of a human life," Ms Turtley-Chappel said.
The teenager had been diagnosed with FASD and Ms Turtley-Chappel said his upbringing had been "incredibly traumatic" and included exposure to domestic violence, homelessness and alcohol abuse.
The defence also highlighted the conditions at the troubled Banksia Hill Detention Centre where he is being held, which included repeated periods of lockdown when he was confined to his cell for hours on end.
The court heard despite the difficult conditions at Banksia Hill, the teenager, who turns 18 soon, would prefer to serve his term in juvenile detention rather than be sent to an adult prison.
Boy left without mother after 'cowardly' offence
The prosecutor, Ms Cullen, said the offence was aggravated by the presence of Ms Miller's eight-month-old son in the car and by the death of her unborn baby.
Ms Cullen described the offence as "cowardly".
"He lay in wait, they were not prepared to defend themselves from the throwing of the rock", she said.
"It did cause the greatest harm, the loss of life of not just Ms Miller, but her unborn baby [and] it left an eight-month-old boy without a mother."
