A pupil who was stabbed to death in an unprovoked attack by a bandana and hoodie-clad gang had recently been involved in a peace project with children from Northern Ireland.
Ajmol Alom (16) was murdered in Spey Street, east London, on Monday night, and a friend of the same age was left with injuries to his face.
Detective Chief Inspector Andy Chalmers said Ajmol was with a "peaceful" group of fellow Bengalis when he was attacked.
Speaking at the scene, he said: "Initial indications are that Ajmol was with four friends. They were peaceful, they were conducting conversations at the location, Spey Street, which is behind me.
"They were then confronted by five to six other males who were wearing bandanas and were hooded.
"There appears to have been an unprovoked attack when the victim received his facial injuries and then Ajmol was stabbed."
Chris Dunne, head teacher at Langdon Park School, said Ajmol was a star pupil awaiting his GCSE results and had a "very bright academic future ahead of him".
He said the teenager had recently taken part in a conflict resolution project with other young people from Northern Ireland, in which he was "hugely active".
"He was a very, very splendid young man," he said. "Hardworking, industrious, but also a caring and thoughtful young man."
A 19-year-old man has been arrested on suspicion of murder.