Rajan Singh, the driver of the bus, lived in Gurgaon village and after school hours parked the vehicle there as a routine, he said.
The bus was parked at the spot, barely 200 metres from the police station, for three days at a stretch due to a string of holidays in the school, police said.
On Wednesday, the driver was taking the bus to school but it broke down on the way in sector 29. The driver while trying to locate the snag stumbled upon the body in the box.
"Only the post-mortem report will reveal how she was killed and whether she was sexually assaulted before her murder," Surender Pal Singh, deputy commissioner of police (west), told IANS.