The Central Bureau of Investigation (CBI) on Tuesday arrested a former Joint Director of the Enforcement Directorate, J.P. Singh, in a corruption case registered by the agency in September 2015.Three others have also been arrested, including ED official Sanjay Kumar and two middlemen Vimal Agarwal and Chandresh Patel.They were arrested from Delhi in a corruption case which was being investigated by the agency since September 2015 when it registered a case on the directions of the Finance Ministry.They were booked under charges of prevention of corruption and criminal conspiracy.