Two more teenagers have been arrested in connection with the murder of 14-year-old Paul Erhahon.
The arrests of an 18-year-old and 15-year-old in east London bring the total of people held over the stabbing to nine.
The pair are in custody at an east London police station, a spokesman for Scotland Yard said.
Paul died from a stab wound to the heart after he was attacked in the foyer of a block of flats in Leytonstone, east London on April 6.
So far, four teenagers have been charged with the schoolboy's murder.
The four boys, aged 13, 14, 15 and 17, are also accused of the attempted murder and grievous bodily harm of a 15-year-old boy.
They were all remanded in custody at Waltham Forest Youth Court last week, and will appear at the Old Bailey on April 24, Scotland Yard said.
Detectives have also arrested a 19-year-old man and two boys, aged 14 and 15, who have all been bailed until June while further inquiries are carried out.
Paul was the seventh Londoner aged under 16 to be murdered since the end of January.
He attended Kingsford Community School in Beckton, east London - the same school as 15-year-old Adam Regis, who was stabbed to death last month.
