Shahbuddin boarded Dibrugarh-New Delhi Rajdhani Express at Naughachia station in Bhagalpur district with a posse of security personnel, Deputy Superintendent of Bhagalpur special jail Ramanuj Kumar said.
Deputy jail superintendent Amardeep Singh, one inspector, two sub-inspectors and about 20 constables accompanied Shahbuddin to New Delhi, he said.
The ex-MP has been taken to AIIMS in the national capital on a court order which had accepted his request for treatment to his acute back problem.
Though his involvement in the murder is yet to be ascertained, Shahbuddin was send to Bhagalpur from Siwan jail amid report of his holding durbar in the jail.
The RJD strongman is facing life imprisonment in two cases.