A £20,000 reward is being offered by police investigating the murder of a teenager three years ago.
Edvin Johnson, 19, was stabbed in the leg in a stairwell in Barnet House on the Crawford Estate in Camberwell, south London, in September 2007.
His mother Genevive Johnson said she was "devastated" and "totally lost" without her son.
Nobody was ever charged over the death and police are now offering the sum for information leading to a prosecution.
A Metropolitan Police spokesman said 12 youths were on the estate at the time of the incident and it is believed five of them attacked Edvin and another man.
His family marked the anniversary of his death with a vigil at the scene.
Edvin was about to start a course in business studies at Southampton University.
Speaking in 2007, Ms Johnson said: "I am so disappointed that no-one has come forward to help me find the killer.
"He was the centre of my life and his death has left a big hole in my life.
"Whoever murdered my son needs to be accountable for their crime. They should not go unpunished."
Three men, one aged 20, the other two 23, had been arrested on Tuesday and have been released bail pending further inquiries.
Twelve others arrested in connection with the murder have been released without charge.