Patna Railway Superintendent of Police Suresh Choudhary said the victim was seriously injured when she jumped out of the Delhi-bound Brahamputra Mail between Bihta and Arastations.
“The Government Railway Police with the help of passengers caught one of the accused at Buxar railway station,” said Choudhary.
He said the arrested man was a soldier in the Indian Army.
The critically injured woman is said to be from Darjeeling in West Bengal and boarded the train at Guwahati in Assam, a police official said.
Choudhary said police were yet to record the victim’s statement as she was in a serious condition.
Inspector General of Police Arvind Pandey said all district superintendents of police and railway superintendent of police had been told to expedite investigation and file chargesheets at the earliest.