The four accused and three others allegedly got into an argument with the conductor, Gurdeep Singh (22) last night, when he was strolling near his house with a friend, police said.
The seven accused attacked Singh with sharp-edged weapons, leading to his death, they said.
All the accused, who are in their twenties, have been identified on the complaint of Gurdeep's friend Randhir, Station House Officer (SHO) Narinder Singh said.
Mohit, Ravinder, Somit and Dinkar have been arrested while the police is on the lookout for the remaining accused, he said.
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Meanwhile, another report from Ambala said a badly charred body was recovered from near Khudda village on Ambala- Jagadhri road.
Assistant Police Commissioner (ACP) Rahul Dev said the body has 100 per cent burns and has been sent to Cantt civil hospital for post-mortem, adding that the age and sex of the victim would be known after the autopsy.
He, however, said a murder case has been registered against unknown persons.
Passersby had spotted the body lying near a school wall and they informed the police.