A 19-year-old college student and his friend have been arrested in connection with the killing of a first-year student of Delhi University, police said on Monday.

The first-year student, Nikhil Chauhan, of the university's School of Open Learning was allegedly stabbed to death on Sunday outside Aryabhatta College in the South Campus after he objected to his girlfriend being harassed by another student.

The accused have been identified as Rahul, a first-year college student and a resident of Delhi's Bindapur area, and his friend Haroon (19), a resident of Janakpuri who worked at a T-shirt factory in the Nilothi area here, police said.

Rahul's father runs a small shop in Bindapur, they said.

The victim, Nikhil, was pursuing BA (Hons) in Political Science and was a resident of Paschim Vihar.

According to sources, on June 11, Rahul, Yash and Raj Singh were present with a girl in the canteen of Aryabhatta College. One Bunty passed a comment on them, following which a scuffle broke out. Meanwhile, Nikhil came there with his girlfriend and tried to intervene, and in the melee, his girlfriend was allegedly slapped by one of them, the sources said.

Later, the matter was sorted out. However, on Sunday, the alleged accused stabbed Nikhil when he came to attend the class, they said, adding that the facts are being verified.

Nikhil received one stab injury in his chest and was rushed to a nearby hospital where he was declared brought dead, police said.

During interrogation, the arrested accused told police that Raj had stabbed Nikhil. The details about the sequence of the incident will be verified after the arrest of other accused persons, the sources said, adding the number of persons involved in the incident might increase.

A case was registered at South Campus police station on Sunday, police said.

Meanwhile, the family members of victim Nikhil alleged that he was killed after a planning. However, police stated that the angle of conspiracy will be verified after the arrest of other persons.

In a video that has surfaced online, the victim's father, Sanjay Chauhan, is seen breaking into tears outside a police station and crying for help, following which he is taken inside by a policeman.

The family members of accused Haroon said that police picked him for questioning on Sunday night.

"Police took Haroon along with them last night and informed us that they will leave him later. However, when we came to the police station in the morning, we got to know about the incident," a relative of Haroon said.

Preliminary investigations revealed that a student of the School of Open Learning allegedly misbehaved with Nikhil's girlfriend around a week ago. When he objected to the harassment, the accused got angry and allegedly decided to take revenge, police had said on Sunday.