The investigation into the fatal stabbing of a teenager at Sydney's Royal Easter Show is being frustrated by a lack of co-operation from potential witnesses.
Police have still not identified the person who stabbed 17-year-old Uati Faletolu on April 11, despite hours spent reviewing CCTV footage of the incident.
Many people witnessed the brawl and stabbing and may have video but are yet to come forward, Homicide Squad Commander Danny Doherty says.
"It's not the time now to stay silent," he said on Tuesday.
Plenty of people may have unknowingly captured footage of the stabbing.
"They may think it's inconsequential but it could be incredibly important to us," Detective Superintendent Doherty said.
"They may have captured unknowingly or inadvertently who is actually responsible for (the) stabbing."
Det Supt Doherty said people may not come forward because they thought they didn't have any useful information, or they felt they had to stay "staunch".
One teenager who had been arrested had not helped the investigation, which the homicide detective attributed to "misguided loyalty".
He said the family of the victim was being as supportive as possible.
"It's the associates of the group that really frustrate us," Det Supt Doherty said.
"There's a 15-year-old who obviously would know and there's a 16-year-old who would know as well. There's other people who would know.
"So far, they've lost their mate and close associate and they're not coming forward."
Misguided loyalties and a code of silence were preventing people coming forward, but now was the time for action, Det Supt Doherty said.
Theories that the brawl may have been pre-arranged between rival groups are a strong line of inquiry.
"But until we know who's involved, we'll never know what the motive may be," he said.
