Government Rail Police (GRP) officials said the incident happened in Barauni-Katihar Passenger train, and the three drugged persons were taken down at Katihar station.
Katihar rail police station in-charge Vijay Kumar Singh said, "The deceased is identified as Ganpati Verma of Balrampur in Uttar Pradesh. He was travelling to Malda in West Bengal. His son Prakash Verma is in critical condition along with another passenger Dinesh Sah of Rupauli in Purnia."
Singh said the three were taken down from the train in unconscious condition after the railway police got information about some passengers being drugged and looted.
Family members of the deceased and hospitalised people have been informed.