Police said they have "narrowed down" on the line of investigations, though they are verifying several points that have emerged during the probe, even as two more people approached police with "relevant inputs". They appealed to witnessed to come forward and help them solve the case soon.

Radhika was shot dead on a foot-over-bridge outside Ramlal Anand College in Dhaula Kuan's Shantiniketan on Tuesday by an unidentified person.

"Some friends and close family members have told us that the suspect's sketch matched with the person who had stalked her some time back. They were aware of a certain incident which happened sometime back," H G S Dhaliwal, Deputy Commissioner of Police (South), said.

"They have told us that the portrait largely resembles the person who was earlier involved in the incident," he said. However, he said, the sketch was prepared on the basis of vague recollection of three persons who saw the attacker running away. "Nobody has seen him from the front... We are verifying it," he said, adding, nobody has been detained in this connection.

He said the family or friends do not know the identity of the "stalker", his residential address or parentage. "We have found certain vital clues and have narrowed down our investigation. We have definite lines on which we are working.

"We would request people who were present there to come forward and talk to us, maybe discretely. Otherwise, the investigations would be long drawn," he said. A senior police official said they were questioning some people who resemble the sketch released by them after general public provided information about them. "We are questioning them. However, we have not detained them. Nobody is under detention," he said.

The official also denied reports that someone identified as Victor has been detained in connection with the case. Dhaliwal said the incident of stalking was not reported to police. "There is a handicap. Nobody knows who he is, where is his residence. There is no documentation of the incident as it was not reported to police. Normally in such incidents people do not approach police," he said.

Preliminary investigations suggested that Radhika's stalker used to stay near her house, he said adding police needs to do more verification on this.

A senior police official said they were in the process of verifying around 3,000 people who had left Naraina village in the past few years. "The village houses a number of fabrics and garment units where migrant labourers from UP and Bihar works," he said.

There were three incidents of locals beating up youths for harassing girls. "We are looking into all these. These are three different cases," he said. Investigators had yesterday expressed dismay that no one, who was present at the scene, has come forward.

Police have ruled out property or monetary angle in the murder which shocked the capital and said it appeared that some personal issue was behind the incident. Meanwhile, the family of a college student who was murdered three days ago today demanded speedy justice for their daughter and alleged that police have not told them about the case.

"Police have not told us anything about the investigation... We only want the attacker to be arrested soon," Radhika's father Rajinder Tanwar alleged. He said his daughter had never told them anything about stalking.

BJP's student wing ABVP has called for a strike in Delhi University tomorrow to protest the murder of a girl outside her college in the capital. According to ABVP Delhi Secretary Rohit Chahal, students of all the colleges affiliated with Delhi University have been asked to participate in the strike. The strike call came during the third day of protests in the campus.

During the protests, students blocked traffic near Delhi University north campus besides burning the effigy of crime. A number of students participated in the protest. Meanwhile Chief Minister Sheila Dikshit rued the indifferent attitude of the passers-by when Radhika was shot dead and asked the civil society to speak up and not remain mute spectators to such incidents.

Asking people and civil society to play a "responsible role" in ensuring safety of women in the city, Dikshit expressed shock that not a single person had come forward to help the girl after she received bullet injuries.

"It was not an isolated place. So many people were there. But none of them either raised voice or came forward to take her to a hospital. It is extremely unfortunate that everybody present there kept their eyes shut and she was taken to hospital only after police van had reached," said Dikshit.

Holding that civil society's indifferent attitude to the incident was really a matter of concern, Dikshit said only police should not be held responsible for such incidents. "The civil society which was present at the spot shut its eyes and said it doesn't matter to me and I am not concerned. This is unfortunate.