Sajid (36), the main accused in the case, was absconding and six raids were conducted to arrest him, DCP (southeast) Romil Baaniya said.
"He was traced in Bijnor during a raid late last night and was brought to Delhi. He confessed to his crime and was arrested this evening," the officer said, adding he is being interrogated to trace the other accused.
The rape victim's mother had lodged a complaint at Jamia Nagar Police Station on December 11 saying her 15-year-old daughter had been raped for over a period of six months.
Yesterday, the rape victim's mother was shot at by unidentified assailants, which she was taking her daughter to a hospital for routine check-up.
She was admitted to AIIMS, operated upon and stated out of danger.
The victim's family alleged that the woman was being pressurised by the accused and also getting death threats to make her withdraw the complaint, even as police said it is to be investigated whether the two cases are linked.