Police investigating the murder of a teenager who was killed in an apparently unprovoked stabbing have arrested a fourth man.
Ajmol Alom, 16, died after he was wounded in the thigh just yards from his home in Poplar, east London, on August 12.
Scotland Yard said a 21-year-old man had been arrested at an address in Tower Hamlets, east London, on suspicion of murder.
It became known on Thursday that Ajmol, who had ambitions to be a doctor, had achieved top grades in his GCSEs.
Friends collecting their own results at Langdon Park School, within sight of where he was stabbed, said they were not surprised Ajmol achieved eight grade As in subjects including maths, science, English literature, geography, religious studies and citizenship, and three B grades in English language, humanities and physical education.
The school's headteacher, Chris Dunne, said: ''Our school, our community, our country has just lost one of its brightest prospects and we are all rightly shocked and depressed by it.
''The best comfort we can take from it is that, for however short a time, those of us that knew Ajmol knew a very splendid young man and a fine citizen.''
A 19-year-old man, Aminur Khan, of Robin Hood Gardens, Poplar, has been charged with murder. A 19-year-old man and a 21-year-old man are on bail to return to police on a date in September.