Edvin Johnson, 19, was stabbed to death in the stairwell of a block of flats in Camberwell, south London, on Sunday 16 September 2007.
The teenager was a few days away from starting a course in business studies at Southampton University when he was attacked at Barnet House on the Crawford Estate at around 9pm.
Detectives believe five youths out of a group of 12 on the estate that evening took part in the assault on Edvin and another man. Neither victim is thought to have been the intended target.
Edvin suffered a single wound to his groin and was pronounced dead on arrival at hospital.
A £20,000 reward is still being offered for information leading to the identification, arrest and prosecution of the person or persons responsible.
In September 2012, Edvin's mother Genevieve Johnson told the Voice newspaper: “People say in time your pain will go but I have not experienced that because we have not had any justice.
“For the young man who took my son, life continues but I'm still in the same place. I just constantly ask myself why? Every time I pass someone in the street who turns their face, I'm thinking ‘that boy must know something’. I have no answers and that torments me.”
Three knives were recovered from the area and one of them had Edvin's blood on it.
It is hoped someone will recognise the distinctive stainless steel blades and come forward to help police.
In a previous appeal for information, DCI Andy Redwood said: "I hope that the youths who were not part of the group that attacked Edvin now have the courage to come forward and speak out against the cowards who committed this offence.
"I would also urge anyone with information, particularly anyone who remembers a knife going missing in September 2007 to contact the incident room. Any information we receive will be treated in confidence."
A total of 16 suspects had been arrested in connection with the investigation. None have been charged.