With these arrests the number of those held in the case, which triggered nation-wide outrage, has reached five but the "prime accused" is still at large, they added.
"We have arrested four more persons, including three youths, aged between 24 and 30 years and a 50-year-old man," Kamaldeep Goel, the Superintendent of Police (SP), Government Railway Police (GRP), Faridabad, told PTI over phone.
The 50-year-old arrested today is a Delhi government employee while the three others were doing some private jobs, Deputy Superintendent of Police (DSP), GRP, Faridabad, Mohinder Singh said.
Goel said that with these arrests, the sequence of events which led to the stabbing of Junaid has also, to a large extent, become clear.
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Junaid (17) was stabbed when he along with his brothers was returning home to Khandawli village in Ballabgarh after shopping for Eid in Delhi on Thursday.
Goel said that it had come to fore that the 50-year-old man had entered into an altercation with Junaid and his brothers over seat sharing.
"However three youths who had boarded the train at New Town Faridabad station also got involved in the quarrel with the 50-year-old man egging them on," Goel said.
Asked if the person who had stabbed Junaid had been nabbed, the SP said the "prime accused" was still at large.
He, however, expressed confidence that "now, we have got crucial leads and he too will be in custody soon".
Earlier today, Haryana Chief Minister Manohar Lal Khattar condemned the incident.
"The action in the case is being taken as per ongoing investigations. Whatever action is deemed fit will be taken," he said.
Asked from where the four accused were arrested today, DSP Mohinder Singh said, "we have questioned several people during the past few days. On the basis of statements taken from some of the passengers in the train, we had summoned a few suspects at the office of the crime branch at Faridabad today. After the role of the four was established, we arrested them".
Junaid was stabbed to death while his brothers - Hashim and Sakir - were injured by a mob which also allegedly hurled slurs against them onboard the Delhi-Mathura passenger train between Ballabgarh and Mathura stations on Thursday night.
Junaid's body was dumped close to Asaoti village in Faridabad district.
Police had earlier announced a reward of Rs 1 lakh for credible information leading to arrest of the accused in the case.
The accused person arrested earlier, while speaking to reporters, had alleged that he was in an inebriated state and had attacked the teenager after being instigated by fellow passengers.
The incident was also condemned by Union Information and Broadcasting minister M Venkaiah Naidu today.
The CPI(M) had also sent a delegation to meet the victim's family.
The delegation asked the police to ascertain the political affiliation of those involved in the "horrific mob lynching" and said the accused would not have dared to target the victim sans "political patronage" in the BJP-ruled state.
Junaid's brothers had told reporters earlier that the attackers taunted and repeatedly called them "anti-nationals" and "beef eaters".