A reward of £20,000 has been offered to find the killers of Adam Regis
The family of a 15-year-old murdered three years ago "have the right to know" who killed him, police have said in a fresh appeal for information.
Adam Regis was stabbed in the chest in Plaistow, east London, as he returned home from a cinema on 17 March 2007.
Although 17 people have been arrested, nobody has been charged.
"There are some people with knowledge of the murder who are not coming forward and speaking to the police," said Det Ch Insp Steve Clayman.
"Hiding the fact you are involved in someone's murder is difficult to live with and Adam's family have the right to know why this happened and who is responsible," he added.
The teenager was stabbed with a knife which had a blade of at least eight inches (20cm) and which went through his right arm and into his chest, cutting his aorta.
The nephew of former athlete John Regis had been out with friends in Beckton and was walking home when he was attacked.
He was found lying injured at the junction of Boundary Road and Kingsland Road, and later died in Newham General Hospital.
A £20,000 reward has been offered for information leading to the conviction of the student's killers.