Officers from the PSNI and Interpol are checking reports that Francois de Dietrich travelled here under a false passport using freight ferries between France and Britain and then between Britain and the North.
The most recent trip could have been just two months ago at a time when a European arrest warrant had been issued.
He had fled a village near Paris last year after his location became known to French police.
“We believe he may have used a DFDS freight route between Belfast and Heysham for the journey to Northern Ireland,” said one PSNI officer today.
“And we believe he may have used that route on several occasions, perhaps as recently as February, before travelling to the North West to Derry and then to Donegal.”
Gardai and the PSNI are keen to hear from anyone who have seen the conman in the North West in recent months.
Francois de Dietrich offered dozens of Donegal investors massive returns if they handed over money to him.
Some people initially made money out of their ‘investment’ but ultimately around €30M was scammed, with police now believing up to €20M of that was taken from people in Co Donegal.
But donegaldaily.com rumbled the scam and de Dietrich fled the country.
However British and Irish authorities moved to freeze bank accounts containing tens of millions of euro north and south of the Border.
In January the French man, who was formerly based in Ballybofey, failed to turn up for a court hearing in Belfast where he was due to appeal an 18-month prison sentence for contempt of court.
The jail term was imposed after he refused to reveal details of his worldwide assets to the UK Financial Services Authority.
His former solicitor in Belfast was given permission by the courts to end representation for him.