A man was arrested and later released by officers investigating the National Assets Management Agency (Nama) sale.
The National Crime Agency is leading the probe into the disposal of the massive Northern Ireland property portfolio.
An NCA spokeswoman said: "On August 24, officers from the National Crime Agency arrested a 54-year-old man at Belfast International Airport in connection with its on-going Nama investigation.
The man was later released on police bail.
"As the investigation is continuing, we are unable to comment further."
Nama's sale of its 850-property Northern Ireland interests is under investigation.
Nama is the Republic's bank for bad debts, which was established following the banking crisis.