Recently-seized documents show that former Polish president and Solidarity founder Lech Walesa was a paid informant for the communist-era secret security between 1970 and 1976.
Mr Walesa has admitted signing a commitment to be an informant but has insisted he never acted on it.
In 2000 he was cleared by a special court.
Lukasz Kaminski, head of the state National Remembrance Institute, said today that documents seized from the house of the last communist interior minister, the late General Czeslaw Kiszczak, include a commitment to provide information to the secret security that is signed with Mr Walesa's name and a codename, Bolek.
There are also pages of reports and receipts for money signed by Mr Walesa.