LONDON — Two Polish immigrants were eating takeout pizza against a brick wall on a muggy night in Harlow, a working-class town about 20 miles northeast of central London.

As they chatted in Polish, witnesses said, a group of young boys and girls attacked them. The group repeatedly pummeled and kicked one of the men, Arkadiusz Jozwik, 40, a meat factory worker, in the head. He died two days later from his injuries, in a killing that the police are investigating as a possible hate crime.

The second man, who was not identified by the police, was hospitalized with bruises and hand fractures.

Six boys from Harlow — five 15-year-olds and one 16-year-old — have been arrested on suspicion of murder in the attack, which occurred shortly before midnight on Saturday. All have been released on bail. The police have appealed for witnesses to come forward, and they said they were investigating reports that the attackers had hurled racist abuse at the victims.