A boy on trial for the murder of a man during a brawl at the Weston Creek Skate Park fabricated a claim that he found a knife on the ground during the fight, prosecutors say.
The 17-year-old, who was 15 at the time, has admitted stabbing the victim's cousin, as he tried to protect his friend in the melee, but denies going anywhere near the man who died.
The court has previously heard that the knife has never been retrieved and the boy said he had dropped it down a drain the next day.
Prosecutor Rebecca Christensen today told the jury that the man's death was a tragedy that should have been prevented.
She conceded no one had seen the boy stab the victim, and the evidence was circumstantial.
But she told the jury looking at the whole of the evidence it was clear that the boy was the only one who had a knife at the skate park that night, and that the number and depth of the stab wounds revealed the crime.
The court heard the fight at the park had been arranged after an angry exchange on Snapchat and originally involved two groups, quickly followed by a third group in a four-wheel drive, who had been called as back up.
Ms Christensen told the jury the most likely chain of events was that the victim, who had been driving one of the first two cars to arrive at the skate park, was attacked by those in the third car, while his cousin who was on the passenger side fought off boys from the other car.
She said the cousin was stabbed during this fight, before a boy got out of the victim's car with what looked like a machete.
The blade turned out to be a toy, which one of the boys had taken in case they needed a deterrent.
Ms Christensen said in the lull as the men from the truck grabbed garden tools, which they used to smash the victim's car, and while everyone's attention was elsewhere, the boy had an opportunity to stab the man multiple times.
She said there was substantial evidence supporting the murder charge, including forensic evidence which showed blood from both victims on the inside waist band of his pants, where he had shoved the knife.
Ms Christensen said there was very little blood on anyone else.
And she said the boy had also made admissions in the days afterwards, with one witness telling the court he overheard the boy say it was him and he would go on the run, and that he was sorry.
Ms Christensen also questioned the boy's account of seeing the victim fighting with the men from the car as he picked up the knife.
She said evidence from the forensic pathologist, Johan Duflou, showed this would have been impossible.
"I suggest [the accused] has fabricated this account of picking up the knife to explain how [the victim's] blood got onto his pants."
The boy gave evidence in the trial, telling the court at first he thought he had killed someone, but neither he nor any of his friends knew who had died.
He said when he saw a police statement of facts two months later and saw the driver had died, he realised he had not killed anyone.
But Ms Christensen has cast doubt on that account, reminding the jury he had told one of the other witnesses he had stabbed someone seven times.
The victim's cousin was stabbed only once, and Ms Christensen said police had been careful not to reveal the man had been stabbed six times, something that only came out in the trial.
But she said that appeared the only possibility.
The boy's lawyer David Barrow will not give his address to the jury until next week.
But he has already told the court he will advance a theory which points the finger at one of the other witnesses, and shows the boy is telling the truth.
