Defence barrister David Barrow labelled this brawler a "shameless liar" in the ACT Supreme Court on Tuesday, when he addressed a murder trial jury for the final time.

Mr Barrow's client, now aged 17, has pleaded not guilty to a charge alleging he murdered an 18-year-old man, who was stabbed six times during a fight at the Weston Creek skatepark in September 2020.

The accused has, however, admitted seriously injuring the deceased's 16-year-old cousin by knifing him in the back during the same two-minute melee, which erupted in response to a Snapchat argument.

None of the people involved in the fight, which involved three carloads of participants, can be named for legal reasons.

Mr Barrow on Tuesday attacked the credibility of four brawlers who went to the scene in a large utility, describing them as "fundamentally dishonest" people who made hundreds of "self-serving statements".

"Each of them is, unfortunately, a shameless liar," he said.

"The lying was brazen. It was obvious."

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The defence barrister asked jurors to consider whether there was a reasonable possibility that one of the people from this utility, a Mitsubishi Triton, had killed the deceased.

Mr Barrow honed in on one, a man in his mid-20s, saying this brawler had minimised his involvement in the incident "to an enormous degree" and told "a quite pathetic lie" about his movements during the fight.

He said this man claimed to have punched the deceased in the stomach early in the piece before moving to the other side of the cousins' car to help a younger brawler.

Mr Barrow described this as "manufactured rubbish" and highlighted DNA consistent with the man having been found "right beside" a stab wound on the deceased's back.

The older brawler's evidence did not explain this, Mr Barrow argued, nor the discovery of DNA consistent with both him and the deceased on the bonnet of a car at the centre of the incident.

"There is a compelling case, on the evidence, that [this brawler] was responsible for what happened," Mr Barrow said.

In the aftermath of the incident, the brawler in his mid-20s captured what has been described as a "horrifying" video at the scene.

While Crown prosecutor Rebecca Christensen SC submitted last Friday that the man would not have filmed the footage or showed it to others had he been the killer, Mr Barrow argued otherwise.

"[With] this person, rationality, logic, clear thinking is out the window," Mr Barrow said.

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The defence barrister said the man had been intoxicated by alcohol, cannabis, methamphetamine and LSD.

This brawler was also much older than everyone else involved in the fight, and he had used a pickaxe to smash up a car while "out of control".

The video he had taken at the scene was, according to Mr Barrow, a trophy depicting what he had done.

"That's what you do with a trophy, you show it to people," Mr Barrow said.

"He was ... really pleased to have been able to do these things."

Mr Barrow also described the older brawler as "an accomplished liar".

"His credibility is zero," he said.

"If there's a medal to be given to the witness who told the biggest number of lies, it's him."

Mr Barrow ultimately said the jury would be left with "profound unease" about what had happened in the area the deceased had been found, and about why the people from the Triton had lied in their evidence.

He said none of those four people were friends of the accused.

"They're not lying to protect him, so why are they lying?" he asked.

Chief Justice Lucy McCallum will now sum up the case for the jury, which will then begin deliberating.

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