"We have arrested Nasir and sent him to judicial custody and are on the lookout for his five accomplices who were party to the crime," Deputy Commissioner of Police (East) Satish Kumar told IANS.
According to the first information report (FIR) lodged late Sunday, the accused abducted the victim July 12 when she was in her boyfriend's car in front of her apartment in the city's eastern suburb.
"The accused, who came in a sedan, forcibly pulled me out of the car and pushed me in the rear seat along with my friend and drove us around the locality.
All along, Nasir first molested and sexually assaulted me after pulling my friend out of the car at a desolate place near railway tracks in Cox Town," the victim said in the complaint.
Claiming that they were policemen in plainclothes, they also threatened to take the victim and her friend to police station if they did not give them Rs.50,000.
"When I told them I did not have that much of cash and pleaded to let us go, they refused and instead sexually assaulted me," the complaint noted.
The victim filed the complaint only after tracking the accused along with the car in the same locality Sunday and alerted the police to arrest him and seize the car.
Nasir's father (Bahadur) is an executive member of the BSP's Karnataka unit.
Bahadur campaigned for the party's candidates in the recent Lok Sabha elections and had also contested unsuccessfully in the 2009 parliamentary polls from Bangalore Central seat.