Smithwick is probably the last of the public tribunals and, like its predecessors, it is taking a lot longer and costing a lot more than anyone had expected.

RTÉ's North-East Correspondent Richard Dowling reports that Judge Smithwick has to decide whether or not to have the tribunal go into 'hibernation'.

When it was originally set up in May 2005 it was believed Judge Peter Smithwick would have his report wrapped up speedily.

The Tribunal's task was to investigate claims a garda or gardai passed information to the IRA which allowed them set up an ambush and murder RUC Chief Supt Harry Breen and Supt Bob Buchanan.

But as with Tribunals no one ever knows where their investigations - or evidence - will bring them. And as for the costs – the most up to date figure for Smithwick is €11m but that is only to June of last year.

It is considerably more now. Just how much more is not known.

The tribunal began its investigative work in early 2006 and began hearing evidence in public in 2011 with the expectation it would be concluded within months.

However, now over a year after the public hearings began they're still taking place – albeit with much less frequency.

The Tribunal was granted an extension last November giving it until May of this year.

As that deadline drew close, the Tribunal sought and was given an extension to November of this year. Now a third extension will be sought, probably till late spring or early summer of next year.

There is little doubt Minister for Justice Alan Shatter will go to the Oireachtas and recommend more time for Smithwick.

Politically it would be impossible to try and shut down this tribunal, especially as it is nearing its conclusion.

To do so would draw much condemnation from Unionist politicians in the north and strong criticism from Downing Street.

Just as answers about State collusion in the the murder of solicitor Pat Finucane have become crucial for his family and the Government, the possibility of garda collusion in the murders of the two most senior RUC officers to die in the Troubles has become a touchstone for the Unionist community.

For years there have been allegations and rumours about garda involvement in the ambush in which the two RUC officers died.

It occurred just minutes after they left a meeting in Dundalk Garda Station in March 1989.

Three former sergeants have been the main focus of the Tribunal's investigation; Detective Sergeant Owen Corrigan, Sergeant Leo Colton and Sergeant Finbarr Hickey.

All three have repeatedly denied the allegations.

While Mr Colton and Hickey were only in the witness box for a matter of hours, Mr Corrigan has been there the longest of anyone called to the Tribunal.

He was unwell for some time and the length of his appearances were reduced to try and maintain ongoing questioning.

But despite this, there was no surprise when his cardiologist stepped into the witness box on Wednesday and said Mr Corrigan would not be available for months.....many months.

He was recovering from an illness and would then be having heart bypass surgery. He would not be available for questioning until March.

So where does that leave the Tribunal and its most crucial witness? The Judge does have some options but they are limited.

He cannot simply proceed without Mr Corrigan's remaining evidence.

The former detective sergeant has a right to have his voice heard and rebut allegations.

It was suggested by Mr Corrigan's own legal counsel, Jim O'Callaghan that any further questions to his client could be written down, he could go get the answers and then deliver them all back to the Tribunal.

This does have the advantage of not having to wait months for Mr Corrigan's return and as most of the legal teams in the Tribunal had already questioned him, there wouldn't be a huge burden left.

However, the disadvantage – and it is a crucial one - is that the Judge cannot watch Mr Corrigan as he delivers his answers, he cannot look him in the eye and gauge the veracity of what is being said.

This option would allow the witness plenty of time to think and give considered answers to difficult questions.

As the possibility of using a video link to his home to give evidence was ruled out by his doctor, Judge Smithwick has few options.

On Thursday the Tribunal will read into the record crucial evidence given by the PSNI about intelligence that has come out since Smithwick started.

There maybe a few other witnesses who could be called but Judge Smithwick has repeatedly said this Tribunal can't go on forever costing the taxpayer millions.

His choice seems to be either go into hibernation till next year or take written answers.

Neither are particularly appealing for all concerned.