A murder investigation has been launched following the death of a man who suffered "traumatic injuries" in an attack at Stratford train station in east London.
John Francis Breen, 53, was found unconscious with "serious head injuries" after the attack on Tuesday evening.
Mr Breen was rushed to hospital but died from his injuries early today, the Metropolitan Police said.
Two 14-year-olds, a 15-year-old and a 16-year-old who were arrested soon afterwards on suspicion of grievous bodily harm remain in custody and are being questioned by police.
Detective Chief Inspector Dave Shipperlee said: "We continue to investigate the circumstances of the incident and are still in the process of interviewing the four teenagers.
"Our sympathies go out to Mr Breen's family and I would like to reiterate our appeal for witnesses to help us piece together exactly what happened."
Mr Shipperlee added: "We have already heard from several people who were at the station, and I would like to thank those who have come forward.
"I am certain there will be more people who cannot only help us with our investigation, but can also provide information that will assist Mr Breen's family in understanding how he sustained such traumatic injuries."
Commuters endured rush-hour travel disruption at Stratford, close to the Olympic Stadium, following the attack after parts of the station were cordoned off by investigating police.