Two youths arrested over the murder of 14-year-old Paul Erhahon are still being questioned at separate police stations in London.
The 13 and 19-year-old males were arrested hours after the attack, and can be held until 0400 BST on Tuesday.
Paul died outside his home in Leytonstone, east London, on Friday after he and a friend, who is critically ill, were stabbed by a gang.
He moved schools last year after he was stabbed by bullies, his aunt 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.
Police said a bladed instrument or a knife was used to kill Paul and injure his friend.
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
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, 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 Rev Alison Mackay, who led the Easter service at Leytonstone United Free Church, said: "There are problems in our community. There is a lack of youth facilities and something needs to be done."
The latest attack follows the killing of at least five other male teenagers in London in the past two months.