A murder investigation has begun following the death of a man who was attacked outside a Tube station after accidentally stepping on a boy's foot.
Mr Prasanna was airlifted to hospital
Vipaul Prasanna, 41, from west London, was pronounced brain dead at 1800 BST on Wednesday, four days after he was punched in the face by a stranger.
He had bent down to apologise to a young boy after apparently stepping on his foot at Wembley Park Tube station.
A man with the boy hit Mr Prasanna who fell, hitting his head on the pavement.
The investigation has become a murder inquiry, said Scotland Yard.
Mr Prasanna worked in a shop in Brixton, south London, and sent money back to his wife and three children in Sri Lanka.
Detective Chief Inspector Colin Sutton said it appeared to have been a "minor disagreement which escalated into an act of violence against a total stranger".
The killer and the boy, aged about 10, walked off towards the Chalkhill estate.