A former CID officer has said it was “common knowledge” among his RUC colleagues stationed at the border in the late 1980s that a garda officer in Dundalk was helping the IRA.

The retired RUC detective inspector, identified only as Witness 70, gave evidence from behind a screen at the Smithwick tribunal.

“It was just common knowledge along the border that there was a problem sitting in Dundalk Garda station,” said the witness, who served in south Down between 1987 and 1992.

The tribunal is investigating allegations of garda collusion in the deaths of RUC chief superintendent Harry Breen and superintendent Bob Buchanan as they returned from a meeting in Dundalk garda station on March 20, 1989.

“I was aware of an officer of An Garda Siochana who was actively assisting the IRA,” Witness 70 said. He said the information was passed to him at a Special Branch briefing, and the officer was named as detective sergeant Owen Corrigan.

Mr Corrigan denies any allegations of supplying information to the IRA. “All our inquiries were consistently leading to units of the IRA who were living in Dundalk,” Witness 70 said.

The witness also said he had met with IRA informant “Kevin Fulton” on four or six occasions in the late 1990s and that Mr Fulton supplied information on drug dealing. He said Mr Fulton “spoke comfortably” about IRA contacts, “which confirmed to me he was actively working with them”.

He said Mr Fulton had the air of a “loveable rogue”.

“But there was also a sinister side to him that you had to be aware of.”

And he said he found the information Mr Fulton supplied “good and reliable”, and had led to convictions.