Gardaí are questioning a mortgage advisor in connection with over €4 million worth of fraudulent mortgage applications.
More than 100 applications have been identified which included false information and bogus documentation.
The investigation by the Garda National Economic Crime Bureau, which commenced following complaints from financial institutions, has been ongoing for a number of years.
Gardaí say the fraud goes back several years and enabled people who did not qualify to secure mortgages from banks and other financial institutions.
Applicants paid varying amounts of money for the creation of false documents which were then submitted to financial institutions.
They paid both an upfront fee and an additional payment when the mortgage was secured.
Many of the mortgages date back over ten years and repayments were being made.
109 suspicious cases involving over €4m have been identified.
The Garda National Economic Crime Bureau searched properties in Rathfanham and Templeogue, seized and examined a large quantity of documents and computers, and arrested the man in South Dublin.
The mortgage advisor is being detained in Rathfarnham Garda Station and can be questioned for up to a week.
Gardaí say some of the applicants have already been prosecuted for deception, a number of other suspects have also been identified and a file is being prepared for the DPP.
