A detective leading the hunt for the killer of a teenager stabbed to death in a street brawl has urged witnesses to be brave and come forward.
David Nowak is the 25th teenager to be murdered in London this year
David Nowak, 16, was stabbed to death in Stoke Newington, north London, on Saturday night.
Police arrested 15 people, aged between 13 and 19. They have been bailed to return pending further inquiries.
Det Ch Insp John Macdonald also urged parents to find out if their child knows anything about the murder.
David was attacked on a housing estate near his home in Stoke Newington after a fight broke out following a birthday party at a community centre in Shacklewell Road.
The teenager was followed to a playground in Somerford Grove and stabbed.
He was taken to the Royal London Hospital suffering from a knife wound that cut into his liver and a kidney but died early on Sunday morning.
DCI Macdonald said: "I wish to point out that there were a number of young people in Somerford Grove who saw David being stabbed.
"They are fully aware of who is responsible and there is a reluctance amongst them to speak to police.
"Without their assistance this case will be difficult to deal with, and I would urge them to be brave enough to come forward.
"I want parents to understand that the police and courts can fully protect your child if they give evidence.
"I am asking you to ascertain what your child knows and then speak to police."
A second boy, aged 15, who was taken to hospital on the night of the stabbing with knife wounds remains in a stable condition.
A further two males also went to a local hospital with stab wounds, although neither was seriously hurt.
David is the 25 teenager to be killed in London in 2007.