Kevin Halligen from Dublin was denied bail pending extradition proceedings to the US.
The US Justice Department alleges Mr Halligen tried to defraud a law firm of $2.1m (€1.4m).
The money was part of a deal to secure the release of two Dutch businessmen who had been arrested in the Ivory Coast. But the court heard he had instead used it to buy a mansion.
Mr Halligen was arrested at a hotel in Oxford yesterday where he had been staying for four months under an assumed name.
Police found five mobile phones, a blackberry and an Irish passport in the room.
He was remanded in custody and will appear in court next Wednesday.
