But the ACT Supreme Court heard on Friday that when he woke up the teenager was dead, having been stabbed in what has been described as "a quick and confused melee" at the Weston skatepark.

In an audio recording played to the alleged killer's murder trial, the father recalled racing to the scene and staring in shock for 12 hours at the spot where his son had died.

The fight is currently under the microscope, with a jury being asked on Friday to consider whether the alleged killer, who has pleaded not guilty to murder, had any opportunity to inflict the fatal injuries.

Defence barrister David Barrow, in his opening address, told jurors it was the 17-year-old accused's case that the perpetrator might be any one of four other people who were present during the incident.

Mr Barrow said the trial was "obviously about a terrible, senseless tragedy" as described how 12 people had descended on the skatepark after a "nasty, protracted Snapchat argument about not very much".

He reminded jurors the accused, who has pleaded guilty to recklessly inflicting grievous bodily harm, admitted having stabbed the deceased's 16-year-old cousin in the back during the two-minute melee that erupted in September 2020 in response to the social media stoush.

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While Crown prosecutor Rebecca Christensen SC has alleged the accused also fatally knifed the 18-year-old, who suffered six stab wounds, Mr Barrow said the jury should consider alternative theories.

The defence barrister pointed specifically at three adults involved in the fight, and the person who drove the men there, saying any one of the quartet had "every available opportunity" to be the killer.

He said the adults had been involved in what might be described as "an ambush" on the 18-year-old victim in the early stages of the incident, around the time the accused had stabbed the younger cousin.

Mr Barrow told the jury the non-fatal stabbing of the 16-year-old occurred on one side of a car and claimed there was no evidence linking the alleged killer to the other side of that vehicle, where the 18-year-old was knifed.

Following Mr Barrow's opening remarks, Ms Christensen played the jury recordings of conversations police had with the dead teenager's parents in November 2020.

Both parents, who cannot be named because their son's identity is suppressed, told police it was unusual for the teenager to go out, especially late at night, without telling them first.

They recalled him being on his PlayStation when they went to bed on the night in question, and the father said he reminded the 18-year-old they needed to be up early the next morning for a family outing.

The father told police that when he was woken by a call alerting him his son had been stabbed in a fight, he ran through the family home in disbelief the teenager was not there. He then rushed to the skatepark.

"I stayed there for the next 12 hours, staring at the area where [my son] was," he said.

At the end of the interview, he told a detective his family had "never been closer" than they were before the fatal stabbing.

"We're one of those old-fashioned families who sit down and have dinner every night," the father said.

"Things were, dare I say it, perfect."

The trial of the alleged murderer, who was 15 at the time of the incident and cannot be named because of his age, continues.

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