Ashwini Kumar (35), a trooper of the BSF's 61 battalion, allegedly molested the 20-year-old woman twice inside the Koraput-Rourkela Intercity Express Sunday, before it reached the Sundergarh district's Rourkela railway station, about 514 km from here, police said.
The woman was travelling in the same coach as was Ashwini, who was allegedly drunk, a senior railway police official told IANS.
He followed the girl to the the toilet and molested her, the officer said. The trooper molested the young woman twice in the train, he said.
The trooper was arrested after the woman lodged a complaint with the Government Railway Police (GRP), the official added.
The trooper is a native of Bihar's Balbag area.