An internal garda investigation is under way into the activities of an officer based in Tallaght who is suspected of selling garda intelligence, the Sunday Tribune has learned. It is the second internal garda probe launched in the past three months in which officers are suspected of selling confidential data.

In October, a garda based in Finglas was arrested on suspicion of selling intelligence to a criminal gang. That investigation is being led by the National Bureau of Criminal Investigation (NBCI).

A senior source said it was a "worrying new departure" that two investigations into corruption were simultaneously under way.

In Tallaght, an internal investigation was launched when it emerged that a garda asked three colleagues on separate occasions to check car-registration details of vehicles for sale at garages on the garda communication computer system, Pulse.

By checking a vehicle's registration, information is available about its crash history, among other things, which can be valuable to those in the car trade.

A senior source said the probe is at an early stage and it has not yet been determined if this garda was making a profit from checking cars' history or whether he was "doing favours" for friends.

The officer under suspicion has been questioned but has not been suspended from his duties at this stage.

Those leading the investigation believe this garda was "taking advantage" of three less experienced gardaí who were "inadvertently used" to check information for him when he told them it was necessary for an investigation.

The three gardaí have been questioned extensively, have cooperated fully, and may be disciplined.

The investigation is being led by senior officers in Tallaght and can be handed over to detectives at the NBCI at any stage but initial enquiries suggest it is not as serious as the alleged criminal behaviour of the garda based at Finglas.

This officer allegedly sold intelligence to Finglas criminals about their enemies, including addresses where they would hide out on occasion, the extent of criminality they were involved in, their associates and other general garda intelligence collated on Finglas gangs following extensive surveillance.

The garda's house in Finglas was raided on 11 October and he was arrested along with his girlfriend. Detectives also found a shotgun at his home.

A file is being prepared for the DPP in this case. It is an offence under section 62 of the Garda Síochána Act 2005 for officers to be involved in the "unauthorised release of data" collated by gardaí.