Uati Faletolu, 17, died following the violent brawl on the evening of April 11 this year.
A 16-year-old boy recovered after being treated in hospital for a stab wound to his leg.
NSW Police have arrested and charged three males in relation to the incident.
Two 18-year-old men and a 14-year-old boy were arrested in Sydney's west over the last week. Each was charged with murder and refused bail.
The brawl is likely to have a lasting impact on the lives of several families, and highlights the potential consequences of carrying a knife, acting Assistant Commissioner Jason Weinstein said.
"We have not only the victim's family that has been devastated by the loss of their child, but you also have a 14-year-old ... whose family is also going to be devastated," he said on Saturday.
"As a society, we need parents to tell their kids - these are the consequences."
Hundreds of families and young people were enjoying the Royal Easter Show at the Sydney Showground when the incident took place, NSW Deputy Premier and Minister for Police Paul Toole said.
"Some of these people even witnessed this," he said.
The Investigation was challenging in the early stages as police were met with "a wall of silence" and struggled to get information, Mr Toole said.
"That's why police had to rely on CCTV footage. They had to rely on social media and they had to rely on on iPhones that had video of the incident," he said.
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