District Collector in-charge S Sundaravadivelou said the case, investigated by local police, would be transferred to the CB-CID.
Muthu, the conductor, and an engineering student, his accomplice, have already been arrested on the charge of abducting and raping the 17-year-old girl on January 1.
The incident coming amid the national outrage over the gangrape of a 23-year-old Delhi girl triggered protests by students organisations, political parties and women volunteers of various outfits here.