Detectives have been granted more time to question two youths arrested over the death of 14-year-old Paul Erhahon.
Paul died outside his home in Leytonstone, north-east London, on Friday evening after he and a friend were stabbed by a gang in the area.
Two males aged 13 and 19, picked up by police within five hours of the attack, can be held until 0040 BST on Tuesday.
Paul's parents changed his school last year after he was stabbed by bullies, his aunt has said.
Jackie Mustapha said her nephew was attacked last year in a "personal quarrel".
A post-mortem examination found Paul had died from a stab wound.
LONDON'S TEENAGE VICTIMS
James Andre Smartt-Ford, 16, shot in Streatham, 3 February
Michael Dosunmu, 15, shot in Peckham, 6 February
Billy Cox, 15, shot in Clapham, 14 February
Kodjo Yenga, 16, stabbed in Hammersmith, 14 March
Adam Regis, 15, stabbed in Plaistow, 17 March
Police said a bladed instrument or a knife was used to kill Paul and injure his friend, who remains critically ill.
The boys were both found stabbed in Crownfield Road, a few yards from Paul's home.
Police believe the pair had been attacked in the foyer of Gean Court, a block of flats in Langthorne Road, in Leytonstone.
Officers have said they are investigating whether Paul's death was gang-related but are keeping an open mind.
Earlier police asked people living near to where Paul was stabbed to death to search their gardens for the weapon.
On Sunday churches in the area offered prayers for the boys and their families at Easter services.
The latest attack follows the killing of at least five other male teenagers in London in the past two months.