As the Smithwick Tribunal resumes sitting, RTÉ's Richard Dowling looks at the journey it has taken so far.

The Smithwick Tribunal only has days to run. The problem is we do not know when those days will be.

There is one key witness still to be cross-examined. Now retired Det Garda Owen Corrigan began giving his evidence to the tribunal last June, but it had to be halted due to his ill health.

He has since had a heart bypass operation and despite repeated attempts by the tribunal to discover his current condition, it is still not known when he will return to the witness box.

He along with two former colleagues, Finbarr Hickey and Leo Colton, have all given evidence to the tribunal and denied passing information to the IRA, which led them to ambush and kill the two most senior RUC officers to die in the Troubles.

Chief Supt Harry Breen and Supt Bob Buchanan were murdered within minutes of leaving a meeting in Dundalk Garda Station in March 1989.

Mr Corrigan remains to be cross-examined by legal teams for the tribunal, the PSNI and the Garda Commissioner among others.

When that is done, the tribunal which has cost many millions of euro, will finally finish hearing evidence.

Then it will be a matter for Judge Peter Smithwick to write his report and send it to the Oireachtas.

The Smithwick Tribunal was originally expected only to last a matter of months. That has now stretched into years.

It has taken its legal team from the area formerly known as "Bandit Country" along the border, to the suburbs of towns north and south, as well as to MI5 headquarters in London.

The tribunal has heard from serving and retired police officers from both sides of the border, from members of the IRA, from agents who worked from British security services within the IRA, from their handlers in the RUC Special Branch and the British Army's Force Research Unit.

We have heard a great detail of how the war was fought – both in the open and in the shadows.

A previously unknown internal garda investigation into collusion between someone within the force and the IRA also emerged, thanks to evidence from a retired RUC officer.

We have also heard claims and counter claims, most recently from the PSNI.

They told the tribunal that current intelligence said former gardaí had been passing information to the IRA.

Unsurprisingly, that is likely to be disputed by the gardaí, but it will be up to the judge to decide whom to believe.

It is worth noting too that we have also not heard from the IRA itself.

Transcripts of meetings with those involved in the ambush and tribunal lawyers have been read into the record, but they will not be attending to give evidence directly.

We will not have the opportunity to examine their claims that they spied on Dundalk Garda Station for a long time from an abandoned house.

But regardless of what has or has not been heard, there are several points that must be borne in mind when considering the Smithwick Tribunal.

It is impossible to underestimate the influence of "national security" in what the tribunal has been – or has not been – told by those currently or formerly in the employ of either state.

Nor is it impossible to ignore history or "point scoring" that has come from individuals in the police forces – aimed both at colleagues within the same force or those on the other side of the border.

The actual definition of collusion is also crucial.

In Northern Ireland, collusion is something pretty close to active participation of the security forces in a particular action.

In the case of the Smithwick Tribunal it is far wider.

In the view of Judge Peter Smithwick, actions or inactions could warrant a finding of collusion.

The threshold is far lower and probably more accurate for that.