A lack of access to crucial MI5 intelligence is hampering garda attempts to find the mole who the Smithwick tribunal says colluded with the Provisional IRA in the murder of two RUC officers.
That intelligence, which was presented to the tribunal at a late stage, was a key factor in determining the outcome of the eight-year inquiry.
It was outlined in private session to Judge Peter Smithwick by a PSNI assistant chief constable. But it is understood it was collected by agents from British security service MI5 during an operation along the Border.
The intelligence was described to the tribunal as "live and of the moment" but was dismissed on the final day of the hearing by a senior counsel for Garda Commissioner Martin Callinan as "nonsense on stilts".
The Smithwick findings, which rocked the garda authorities, have cast a cloud over Dundalk station where RUC Chief Supt Harry Breen and Supt Bob Buchanan had been visiting for cross-border security talks before they were ambushed and murdered by IRA units.
Gardai are now anxious to uncover the identity of the person or persons blamed by the tribunal for a leak of information leading to the deaths of the two police officers.
However, their lawyers were given no opportunity to either examine or challenge the evidence because they were excluded when the information was given to the tribunal.
Gardai are examining their position on whether they can seek access to that intelligence to allow their 'mole hunt' to make progress.
At the moment, it is not clear when or how the intelligence was gathered and whether its reliability had been fully tested before it was given to the tribunal.
Serving gardai are reluctant to comment in the wake of the tribunal findings.
But their views have not changed since the garda position was spelled out on the last day of the hearing by senior counsel Diarmaid McGuinness, who pointed out that PSNI assistant chief constable Drew Harris had told the tribunal there was no RUC intelligence at the time of the murders that suggested collusion by any member of the gardai in the ambush.
But now, 24 years later, the tribunal was faced with a wealth of intelligence, which was said to exist and to be all accurate.
Mr McGuinness reminded Judge Smithwick that the intelligence had been withheld from him. "You haven't seen it in its raw, unredacted form or even in a redacted form. You haven't seen any of the documentation connected with it, don't know the identities of the handlers, the grading of the intelligence or when these pieces of intelligence came into their possession," he said.
He said it was inexplicable the PSNI had not shared this intelligence, and was in marked contrast to the everyday exchange of sensitive intelligence, which had been occurring over many years to protect all of the people of Ireland.
Since that statement was made last June, nothing has changed and gardai remain in the dark as to the answers to any of the queries raised then.