Gang members have been asked to break their silence, come forward and help bring the killer of Solomone Taufeulungaki to justice.
Victoria Police on Sunday asked gang members involved in the Deer Park killing to look within their own consciences and help them identify the person who stabbed the teenager.
The 15-year-old died on Tuesday after he and his cousin were allegedly approached by a group of about 10 youths armed with knives near Brimbank Shopping Centre.
Seven boys, aged between 13 and 16, have been charged with violent disorder and affray but no one has yet been charged with Solomone's death.
"This is an act of senseless, cowardly and extreme violence in public and in daylight hours," Detective Inspector Tim Day said.
"It's resulted in the death of a teenage boy who had his whole life ahead of him. His family will never see him grow up, finish school, have a career, create a family of his own."
Calling for public help on Sunday, Victoria Police said they believed the fatal affray was a result of tensions between two youth gangs in the western suburbs.
It is believed the attack on the teenager is linked to an assault that occurred at the Brimbank Shopping Centre the day before Solomone was killed.
"We know many of those involved simply had miscarried feelings and they were just defending their mates with no intention to kill anyone," Det Insp Day told reporters.
"However, at least two people took knives to that incident on Tuesday."
Police have identified the gangs involved and spoke to some of the members involved in the stabbing.
Claiming some of them had had the character to indicate to police who it was that stabbed Solomone, Detective Inspector Day said there was a risk the killer would not be apprehended.
"Unless Solomone's killer is brought to justice, Solomone's blood is on the hands of all that attended at that incident on Tuesday," he said.
"This is not about one side versus the other, this is not about being a snitch. This is about justice for Solomone, this is about doing the right thing."
Detectives believe some people have mobile phone footage of the fatal attack and are appealing for them to contact police.
Officers also want to hear from drivers in the area between 3.30pm and 4.30pm on Tuesday who may have captured dash cam footage of the incident.