Officials of the National Investigation Agency (NIA) conducted an inquiry with a passenger at Tiruchi international airport upon his arrival from Sharjah on Tuesday morning. The passenger, identified as S. Assak Ahmed from Thanjavur, landed here by an Air India Express flight. Police sources said Ahmed had gone on a tourist visa to Dubai where he is alleged to have indulged in some suspicious activities. The detailed inquiry went for several hours before he was let off after confiscating his mobile phone.