Gardaí arrested a man in south Co Dublin today as part of a massive money laundering inquiry involving police in the North, Scotland and England.
He is being linked to high-level insurance and mortgage fraud involving up to 500 houses.
Documents were seized in raids this morning in Dublin and Belfast. Properties in Ballymena and Lisburn in Co Antrim and Bangor, Co Down were also examined.
Detectives believe the racket has been built up using the proceeds of the drugs trade and money laundering.
A spokesman for the Police Service of Northern Ireland said: "This is part of a protracted investigation which has been ongoing for several months."
Around 10 raids were carried out in south county Dublin as officers from the Republic's Criminal Assets Bureau moved in.
Homes, businesses and warehouses were searched early this morning. A source in the CAB said: "The Bureau (CAB) is conducting a series of searches in relation to criminal conduct of an individual in south Co Dublin and its associates."
PSNI financial investigators, the Garda, the Criminal Assets Bureau in the Republic and the Serious Organised Crime Agency were all involved.
The operation was led by gardaí but co-ordinated by the Soca which was established this year to target some of the estimated stg£1 billion being lost to economic criminals throughout the UK every year.
Today's raids were carried out under the Proceeds of Crime Act.
Garda identified more than 20 premises to be raided as part of the investigation including homes in Co Wicklow.
A Garda spokesman said: "A number of places have been searched and are still to be searched here in the Republic, in south County Dublin and in Wicklow."
The investigation in England centred on Barrow-on-Furness in Cumbria.
Additional Reporting: PA