David Joslin, 23, was on his way home from a work Christmas party
A man has died after being badly injured trying to break up a fight between two groups as he walked past them, police have said.
David Joslin, 23, was attacked in the early hours of Sunday 20 December in Chingford Mount Road, east London.
The passer-by got involved after a row broke out by a jewellers' shop nearby.
Mr Joslin, who had been at a work Christmas party, was not thought to have been with either of the groups, The Metropolitan Police (Met) said.
A group had been in the nearby Obelisk pub before getting into a fight in the street with three men and a woman.
Mr Joslin was hurt when he tried to intervene.
He was firstly taken to Whipps Cross Hospital and then to National Hospital for Neurology and Neurosurgery in Queen Square, central London.
He never regained consciousness and died on 27 December.
"Witnesses have said that David tried to intervene as a peacemaker, however he was punched to the floor and knocked unconscious," a Met spokesman said.
An incident room has been set up but no arrests have been made and a post-mortem examination was being held on Monday at East Ham mortuary.
Det Insp John MacDonald, who is leading the inquiry, said police had spoken to several people who had been in the pub, but no-one from the second group had come forward yet.
"I'm sure they are local people, and with the CCTV that we are now collecting from shops in the area I am confident we will identify them," he said.
"It's very obvious from the flowers left at the scene that David has died and this other group will know that now," he added.