A suspected LTTE cadre, who landed in nearby Mandapam after travelling by a plastic boat from Sri Lanka, was arrested on Sunday, police said.
Muralitharan (39) was picked up from Mandapam and police were interrogating him to know about the purpose of his visit.
The Sri Lankan was traced in Mandapam after the police found an abandoned boat off Mandapam coast last evening.
The man had actually jumped off from the boat at a point one km away from the coast and reached Mandapam by swimming, police said.
The detention of the man comes close on the heels of the arrest of the head of the LTTE's 'procurement module' Thambianna alias Daniel (46) in Chennai.
Daniel, who was arrested on July 30 by the "Q" branch, intelligence wing of the state police, had clandestinely landed in Rameswaram by a ferry from Sri Lanka before reaching Chennai.