The State is expected to pay over €18 million to cover the costs of the inquiry into the fatal shooting of John Carthy in Abbeylara Co Longford over six years ago following Mr Justice Robert Barr's decision that the State should pay costs for all third parties to the tribunal.
The tribunal's report, to be published today, will confirm that Mr Justice Barr, who chaired the tribunal, has decided that the costs of those who appeared before it should be paid by the State.
The costs incurred by the State amount to €10.2 million, covering the legal teams employed by the tribunal and the State itself.
Third-party costs are estimated at up to €8 million.
The tribunal began its hearings in January 2003, almost three years after John Carthy (27), a building worker who suffered from manic depression, was shot dead outside his home by two members of the Garda Emergency Response Unit on April 20th, 2000.
The hearings continued until December 2004 after taking evidence from 169 witnesses.
The report was initially expected in June 2005, and no reason has so far been given for the delay in publication.
Mr Carthy died after he was shot from behind by gardaí as he left a house at Abbeylara following a 25-hour siege.
Mr Carthy fired shots from the house during the siege, and was carrying a shotgun as he walked down the road towards Abbeylara before being shot. The tribunal's investigations centred on the Garda's handling of the siege and the chain of command at the scene.
It questioned the failure to bring psychiatric professionals and a solicitor to the scene at an early stage. It heard evidence from the two members of the Garda Emergency Response Unit (ERU) who fired the shots.
Mr Justice Barr looked at the training of gardaí for siege situations and the training given to ERU members.
He heard evidence from gardaí, medical and legal experts, journalists and Mr Carthy's family and friends.
He also examined the Garda's handling of the press at the scene, and he questioned the reasoning behind withholding cigarettes from Mr Carthy.
The tribunal heard evidence from gardaí up to assistant commissioner level, family and friends of Mr Carthy, former employers, doctors, including his psychiatrist, journalists and several expert witnesses who dealt with policing and medical matters.
The report is to be laid before the Oireachtas today, following which it will be made public.
Opposition TDs, including Labour leader Pat Rabbitte, have criticised the Government over the delay in publishing the report.
Mr Rabbitte last month accused the Government of deliberately stalling the publication of the report until after the Dáil summer recess. However, Tánaiste Mary Harney said the Oireachtas would debate the report as soon as possible, and a Dáil debate is expected when the Dáil resumes in the autumn.