Gardai are trying to establish if dissident republicans were involved in the theft of a tanker filled with thousands of litres of laundered fuel from an Irish army barracks.
An internal investigation is also under way by military police to determine how the thieves gained access to Aiken barracks in Dundalk before ramming the front gates with the tanker and escaping.
The tanker, which contained 20,000 litres of illegal fuel, had been seized by Customs officers in a raid on a commercial yard at Longfield, about a mile outside Castleblayney, Co Monaghan, last week.
Investigators said last night that many of the launderers along the Border had close connections to subversive groups and were known to use the paramilitaries in the past to provide "muscle".
Footage from CCTV cameras at the barracks has been handed over by the military to the gardai.