The former senior police officer responsible for investigating the 1974 Dublin and Monaghan bombings has said he received access to never-before-seen top secret material.
Iain Livingstone is leading a number of historic investigations into the Troubles.
These include Operation Denton, an investigation into the Glennane Gang, which was a group of loyalist paramilitaries, and rogue soldiers and police officers.
They are blamed for approximately 120 sectarian murders in the 1970s and 1980s, and are suspected of carrying out the Dublin and Monaghan bombings.
This week some fifty years ago 34 people died after three no warning car bombs exploded almost simultaneously in Dublin during evening rush hour.
A fourth bomb exploded in Co Monaghan around an hour and a half later.
It is the deadliest attack of the Troubles, but nobody has ever been brought to justice.
Persistent allegations of collusion between the killers, and the British security and intelligence services have been made over the years.
However, previous investigations have been stymied by the British government's refusal to release key intelligence documents.
Speaking on The Forgotten, a special RTÉ Radio series marking the 50th anniversary of the bombings, Mr Livingstone said: "Operation Denton has had access to secret and top secret material that no other previous investigation ever has.
"The information we have obtained gives us as thorough and as detailed a picture as would be possible to get."
He said he thought the investigation has "seen everything that exists up to and including top secret cabinet meetings of the British government".
"We've seen all intelligence reports that would sit within MI5 and Legacy Special Branch. We've seen all the information that was going between the north and south.
"We've pieced that together".
He added: "We've also spoken to people that have come forward and provided additional information at times to fill some of those gaps.
"As best as I can judge, we have seen all information that's there to allow us make a full report on the circumstances around the Glennane series."
The former head of the Scottish Police also confirmed how the Operation Denton team have approached "subjects of interest", people who have would previously engaged in paramilitary activity.
The Operation Denton report is expected early next year and follows the Operation Kenova report into Freddie Scappaticci, the IRA agent known as 'Stakeknife', and his British army handlers.
"I would like to conclude the Denton report by the end of this calendar year and I would like to be reporting on it in the early part of 2025," he said.
Meanwhile, Tánaiste and Minister for Foreign Affairs Micheál Martin has said he believes the Operation Denton report should lead to a renewed push from both the Irish and British governments to investigate what happened.
"It would be very important particularly after the publication of Operation Denton that we make one final effort collectively, the two governments, to get to the bottom of it," Mr Martin told The Forgotten.
The Dáil unanimously passed a motion on three separate occasions calling on the British government to release all intelligence documents it holds connected to the bombings.
"'I believe they could and I believe they should [release the documents]. I'm hoping Operation Denton might help and contribute to the families getting some sense of closure," he said.
Mr Martin confirmed An Garda Síochana has co-operated fully with Operation Denton and handed over all documents it has on the bombings, including intelligence files, to the Denton review team.
"I've been clear about the need for full transparency from our security forces, including An Garda Síochána," Mr Martin said.
"Now the quality of information provided - and the degree to which it is catalogued and so on, there might be some issues there," he added.
The Forgotten, from Barry Lenihan and Ciaran O'Connor, continues tonight at 6:30pm on RTÉ Radio 1 and will broadcast tomorrow and Wednesday at the same time.
It will also be available on podcast platforms.
