A fourth accused who played a key role in the Telangana phone-tapping case has been arrested. After prolonged questioning at Banjara Hills police station in Hyderabad, the former Deputy Commissioner of Police at the Commissioner's Task Force, P Radhakrishna Rao, has been taken into custody, sources said. Mr Radhakrishna was the chief security officer to former Chief Minister K Chandrashekar Rao, or KCR, and was later the special task force chief in the city.