Senior politicians who had secret offshore bank accounts used the tax amnesty to escape being exposed as Ansbacher account holders, gardai believe.
Some of the Fianna Fail and Fine Gael politicians named by a whistleblower in the Ansbacher dossier had immunity due to amnesties arranged by the Fianna Fail-led governments in 1988 and 1993, it is claimed.
Meanwhile, a series of fresh revelations about the Ansbacher dossier strengthen claims made by whistleblower Gerard Ryan to the Dail Public Accounts Committee. They include:
* Charlie Haughey's name is on the list of nine senior politicians whom a bank official claims held Ansbacher accounts in the 1970s. Mr Haughey's Ansbacher account was actually revealed in 1997, but only through the McCracken Tribunal;
* The Department of Jobs has confirmed Mary Harney wound up the investigation into Ansbacher accounts, at a time when Mr Ryan was looking into the alleged involvement of former Fianna Fail and Fine Gael ministers;
* The Revenue Commissioners has admitted Mr Ryan's work did alert them to some cases of offshore account holders who were not unearthed by original Ansbacher report.
Mr Ryan claims the former Fianna Fail and Fine Gael politicians held the offshore accounts to avoid tax, but were never named publicly.
He says the list was passed to him by a bank official who worked at Guinness & Mahon, the bank at the centre of the Ansbacher affair.
Mr Ryan included the names in a report passed to gardai and the Revenue eight years ago.
Senior gardai involved in the investigation believe a number of those politicians availed of the tax amnesty.
Mr Ryan claims his probe was focusing on these politicians when he was instructed to conclude his investigations quickly.
The Department of Jobs last night said it was the decision of Ms Harney, then Tanaiste, that led to Mr Ryan's investigation being wound up in 2004 against his wishes and the files passed to the Gardai, Revenue and Tribunals of Inquiry.
"It is important to note that the then Tanaiste received legal advice from the Attorney General (the late Rory Brady) before directing that the authorised officer be directed to complete his investigations in a reasonable time and disclose all books, records and information to all competent authorities," a spokesman said.
The department also confirmed elements of the whistleblower's story, which were revealed by the Irish Independent yesterday.
It confirmed there had been discussions with Mr Ryan regarding possible future assignments, but insisted no specific job offer was made.
Mr Ryan claimed he was encouraged to move jobs in 2001 and 2002, with possible roles at the Office of the Director of Corporate Enforcement, the IDA or the Revenue Commissioners being mentioned to him.
If he had moved jobs he would no longer have been investigating Ansbacher.
The department also confirmed that its then-secretary general, Paul Haran, offered Mr Ryan a "completion bonus" in the early 2000s.
It said this was done because there were concerns the Moriarty Tribunal would have concluded its work without having the benefit of a final report from Mr Ryan, who had already been investigating matters for several years. Mr Ryan claimed he was offered a €10,000 bonus to bring his investigation to a speedier conclusion in 2001. When he did not accept this, he claims to have been offered a bonus of €20,000, which he also ignored. Mr Ryan's allegations were investigated by a team of officers from the Garda fraud bureau in 2007.
After consultation with lawyers from the Director of Public Prosecutions' office, it was determined there was insufficient evidence to back up his claims.
Gardai interviewed several witnesses, including relevant staff at Guinness & Mahon bank. Some of the potential witnesses had died in the meantime.
But they did not interview Mr Ryan. This was left to Revenue staff as part of their inquiries.
Guinness & Mahon was regarded at the time as the saviour of those with a lot of money to invest.
Those who availed of the amnesties did not have to say where they had stashed the cash prior to coming forward.
They made a declaration, giving their name and the amount of money they were handing over to the Revenue, but did not give a history of where the cash had been.
Following this self-declaration, they were given a tax-clearance certificate, showing they were tax compliant, and then allowed to start afresh.
At one stage, thought to be in the final days of the first amnesty, gardai had to provide an armed escort for people turning up with bags of cash, and queueing to hand in the money to the Revenue.
During the fraud bureau investigation, they took details of Mr Ryan's allegations, made inquiries about what he had alleged and then held consultations with the DPP's lawyers on their next move.
The consensus was that there was insufficient evidence in terms of a criminal offence and that ended the investigation.
Mr Ryan put together a new document in the past couple of years and has produced this to the Public Accounts Committee.
In his dossier, he says a former senior official at Guinness & Mahon told him of a "ledger of regular posted transactions" to the Cayman Island Accounts kept in what was known as the "Black Briefcase".
On a number of occasions in 1977 and 1978, the official had sight of a list of names and account balances in the "very secret Cayman ledger and that the account holders included well-known Fianna Fail TDs".
The name of the former Fine Gael minister appears elsewhere in the dossier.
After 1979, the "Black Briefcase accounts" were looked after by another staff member, and the previously identified official had no further involvement.