Om Vir Singh 'Fauji', a retired army man who was the vice-president of BJP unit in Mirapur town, was shot dead by two assailants on Tuesday.
Circle Officer Mahesh Mishra said that 20 people have been taken into custody in connection with the murder and the accused will be arrested soon.
Police have registered a case against two unidentified persons in the case. 47-year-old Singh, who had a licensed revolver with him, had also fired back at the attackers but they snatched it from him.
The criminals had shot Singh with his own revolver before fleeing with the weapon, they said. Following the incident, Singh's family members and BJP workers had staged protests and blocked a road.
Security has been tightened in the area and extra police force deployed.