An investigation by New Haven police and the FBI has concluded a racial slur heard on the police radio was not uttered using a New Haven Police Department radio, authorities said. Police said Wednesday that the FBI had finished a four-month joint investigation with police into the racial slur heard on the police radio frequency Dec. 30. Police said the radios are incapable of producing the identification signal that was detected. Dean Esserman, New Haven police chief, said the incident shook and offended every member of the department and required a thorough and vigorous investigation. Efforts continue to identify the person responsible.