The youth has been identified as Vinod Singh.
The 17-year-old girl, who complained of harassment, was a close friend of the boy with whom he allegedly had a one-sided affair, a senior police officer said.
While police have started an inquiry into the matter and suspect that it is a case of suicide, Vinod's family has alleged "foul play".
During questioning, it turned out that the girl was his close friend for the past three years and their families were next-door neighbours. It also emerged that the girl had complained about the boy earlier too but never insisted on getting a case registered, an officer said.
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Prima facie, the problem was being caused by a one-sided affair on part of the boy. However, the girl later gave in writing that she wanted the boy to be reprimanded by the police for his act but did not want to get any case registered on the basis of her complaint, the officer said.
Vinod's friends were waiting outside. However, he did not join them and walked away in a different direction. Police claimed that they did not go after him as he was not an accused in any case.
Around 8.30 AM today, Vinod's body was found on Nangloi railway track, not very far from the police post and his residence, cut into two pieces. The railway police reached the spot and initiated an inquest.