The 16-year-old, who was described as a star pupil with "a very bright future" ahead of him, was stabbed in the leg after he and his friends were confronted by a gang wearing hoods and bandanas in Spey Street, Poplar, east London, at 9.50pm on August 12.
Ajmol was badly wounded in the thigh, while a friend of the same age was stabbed through the cheek.
Both teenagers were taken to an east London hospital for treatment, where the keen boxer died.
A 21-year-old man arrested on Saturday on suspicion of murder has been bailed to return to an east London police station on a date in mid-September pending further inquiries, the Metropolitan Police said.
Two men - one aged 19 and the other 21 - who were arrested in connection with the investigation also remain on bail.
Aminur Nazir Khan, 19, from Poplar, has been charged with murder and attempted murder.
It was confirmed last week that Ajmol, who was described by his headteacher at Langdon Park School in Poplar as "one of our brightest pupils", had achieved top grades in his GCSEs.
The teenager achieved eight grade As in subjects including maths, science, and English literature.