A man has been arrested in connection with alleged surveillance of Garda headquarters in September.
The 23-year-old man was arrested in Dublin yesterday. He is being held at Ballymun Garda Station.
In September, two men were also arrested after officers from the Special Detective Unit appeared to foil an attempt to spy on An Garda Síochána's Dublin Headquarters in the city centre.
Detectives investigating the activities of dissident republicans searched a room in the Harcourt Hotel and found surveillance equipment, including a digital camera.
Images taken from the seized camera were of serving officers, as part of what detectives believe was an attempt to gather information about gardaí.
The hotel is across the road from the building housing the garda specialist units, the National Bureau of Criminal Investigation, Organised Crime Unit, the Garda Bureau of Fraud Investigation and the Special Detective Unit.