Four people arrested over the fatal stabbing of a 15-year-old boy in north London have been granted police bail.
Negus McClean was attacked in Westminster Road, Edmonton, on Sunday.
Police said they were looking for 13 young black men seen on mountain bikes chasing Negus before the attack.
Two men, aged 18 and 20, and a 14-year-old boy were bailed to return to a north London police station on 6 May. A 16-year old boy was bailed to return to to the police station on 18 April.
The victim, who lived in Edmonton, was stabbed several times and tests showed he died from a stab wound to the heart.
His family have said he was stabbed as he tried to protect his younger brother.
Det Ch Insp Steve Clayman said: "We continue to seek witnesses and those with information about who was responsible for this murder.
"It is vital that the public, and especially young people, have the trust and confidence to speak to the police in these situations."
Negus, described as intelligent and mature, was the fourth teenager to be stabbed to death in London this year.