MEP Mick Wallace is calling on the Government to launch a full criminal investigation into the workings of Nama in the Republic of Ireland.
His comments come after two men were charged in connection with the UK National Crime Agency (NCA) investigation into the sale for £1.2 billion of the organisation's Northern Ireland property loan book.
Speaking to the Sunday Independent from Brussels last week, Mr Wallace said: "In the south, the Cooke report was established in 2017 and is due to report in September, but it's not a criminal investigation. It's only taking a general look at what went on. We need a full criminal investigation into the workings of Nama in Dublin.
"I have a big question: why didn't the Department of Finance, why don't three successive governments, want to know what went on? Because the truth is problematic for them.
"I will not let it rest until Nama is held to account. I have spoken to a lot of the developers who have had experiences and I learned a lot from them.
"I worked hard to try and expose the truth, but it was very difficult given the government didn't want the truth to come out."
He added: "Gardaí have told me it was difficult for them to get inside of Nama to go through everything."
Mick Wallace also revealed he is writing a book on the organisation. "It will be different to anything else that has been said to date," he said.
Last week, the North's Public Prosecution Service (PPS) confirmed two men, aged 78 and 49, are to face fraud charges in the North. Though not named by the PPS, lawyers for the two men identified them as Belfast businessman and former banker Frank Cushnahan and lawyer Ian Coulter.
Mr Cushnahan was secretly recorded while allegedly accepting a £40,000 cash payment from a Nama borrower. He denies all wrongdoing.
At the time, the recording - reported by BBC's Spotlight programme - put another man into the centre of the allegations: former head of Nama's asset management in Ireland, Ronnie Hanna.
In the clip, Mr Cushnahan alleged he had influence over Mr Hanna. He also suggested that he would have Mr Hanna's assistance in getting the developer's loans out of Nama in return for a fee.
"Ronnie and I are thick as thieves," he told the property developer.
In March 2016, both Mr Hanna and Mr Cushnahan were arrested on allegations of fraud by the NCA and subsequently released on bail.
Mr Hanna, like Mr Cushnahan, has strenuously denied all wrongdoing, but if Mr Cushnahan's secretly recorded claims are true, it brings the scandal to Nama's Dublin headquarters.
Mr Hanna was central to the organisation's operations in Dublin and reportedly had the power of 'life or death' over developers, overseeing the sale of assets belonging to Ireland's biggest names - including Derek Quinlan, Michael O'Flynn, Treasury Holdings' Johnny Ronan and Richard Barrett, Harry Crosbie and Joe O'Reilly.
All lost heavily when Nama sold off Ireland's crown jewels - including a stake in Battersea Power Station, the Knightsbridge Estate, and a major stake in the world-famous Claridge's, Berkeley and Connaught hotels - for knock-down prices to vulture funds and international investors.
The decision to take out Treasury Holdings, in particular, raised serious questions at the time about Nama's conduct.
In 2012, when Treasury appealed the decision against the State agency's bosses who had called in their loans, Ms Justice Mary Finlay Geoghegan ruled in favour of Nama and Treasury Holdings lost on a 'technicality'.
However, in her written summary, Ms Justice Geoghegan was highly critical of the State agency, saying that she found it acted unfairly and unreasonably because it did not fulfil its obligation to give a fair hearing to the developer's proposals, which could have saved the company.
After the findings, Mr Ronan's chief legal counsel, Rory Williams, wrote to then finance minister Michael Noonan and raised grave concerns regarding Nama's actions.
London's iconic Battersea Power Station, which the State agency sold for €477m, is now expected to generate profits of up €10bn.
Separately in 2013, developer Paddy McKillen confirmed he had made a complaint to gardaí about Nama in relation to improper behaviour by officials.
And further controversy was to follow in 2018, when the agency apologised "unreservedly" to developers Michael and John O'Flynn for former Nama employee Enda Farrell's leaking of their personal and business information to a third party in 2012.
The agency attracted criticism again in March of this year, when the State's spending watchdog criticised Nama over its handling of the sale of loans linked to Quinlan Private, the property investment group that was run by financier and one-time tax official Derek Quinlan.
Seamus McCarthy, the Comptroller and Auditor General, suggested the agency's mistakes may have cost the State up to €29 million.
Mr McCarthy said "errors and poor analysis" by Nama led to the Project Nantes portfolio being sold at less than half of what its target price should have been.
Meanwhile, on the criminal investigation, this weekend Mr Wallace said Nama is trying to keep the controversy away from its Dublin office.
He said: "If Nama in Dublin are exposed for what they did, it would have phenomenal implications for businesses in Dublin.
"It's the people in Dublin that need to be held to account. That's where it begins and ends."
In recent years, Nama has argued that it returned a profit of over €3.5bn back to the State when cleaning up bad loans and distressed property assets, but in placing the assets on the market at fire sale prices, critics say the real value of the assets have amounted to a €40bn loss to Irish taxpayers.
Despite the national mood 10 years ago reflecting an attitude to, as the then finance minister Brian Lenihan put it, pursue developers "to the ends of the earth", most of the money from the sales would have gone to Irish taxpayers.