A man who died after being punched and knocked unconscious in the street was a passer-by who was acting as "a peacemaker" in an argument between two groups, police said.
David Joslin, 23, was attacked in the early hours of Sunday December 20 in Chingford Mount Road, east London.
A Met Police spokesman said Mr Joslin, who had been at a works Christmas party, got involved after a row broke out outside a jewellers shop in Old Church Road, Chingford.
One group had been drinking in the nearby Obelisk pub before getting into a fight in the street with three men and a woman.
A police spokesman said: "Witnesses have said that David tried to intervene as a peacemaker, however he was punched to the floor and knocked unconscious.
"He was taken to hospital but never regained consciousness and died on Sunday December 27."
A post-mortem is being held today at East Ham mortuary and an incident room has opened at Barking under DCI John MacDonald. No arrests have been made.
Mr MacDonald said police had spoken to several people who had been in the pub, but no-one from the second group had come forward yet.
He said: "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. I would ask that they make contact with us and give an account as to what happened.
"It's very obvious from the flowers left at the scene that David has died and this other group will know that now. If they don't contact us we may have to publish CCTV images in due course and make arrests when we identify them."
Anyone with information should contact the incident room on 020 8345 3985 or anonymously to Crimestoppers on 0800 555 111.