Ashok Makwana, the accused, is a labour contractor.
Based on a complaint filed by the girl's parents, police today arrested the 41-year-old Makwana, said inspector V R Patel of Sardarnagar police station.
Makwana has been booked under section 354-A of IPC (sexual harassment) and sections 11 and 12 of the Protection of Children from Sexual Offences (POCSO) Act.
The FIR lodged by the parents on Sunday said a male passenger sitting next to the girl sexually harassed her during the journey.
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"After she told her parents about the ordeal on reaching home, they lodged FIR against an unidentified passenger. We got the list of passengers and zeroed in on Makwana," he said.
President of Gandhinagar unit of BJP, Mahendra Patel, confirmed Makwana's association with BJP.
"Makwana was offered the post of vice president of city unit recently but he declined citing his busy schedule. At present he is not holding any post in the party," he said.