Police were investigating yesterday a suspected human-trafficking ring in northern Greece after an off-duty border patrol guard was caught listening to police radio frequencies near the airport of Ioannina, close to the border with Albania. Sources said the suspect was arrested near the airport on Friday after being spotted with the radio equipment. When police approached and instructed him to go to the station, the suspect violently pushed them away and tried to escape, said one police source. The suspect was expected to be charged late yesterday with resisting arrest and violating communication laws. Authorities also arrested two other men, both Albanian nationals, as they continue to question border patrol guards in what they suspect is a well-organized people-smuggling racket operating between Greece and Albania.