Polish prosecutors will on Tuesday present what they believe is proof that Solidarity freedom hero Lech Walesa collaborated with the communist-era secret police, the national news agency PAP reported.

Citing unnamed sources close to the Institute of National Remembrance (IPN), which prosecutes crimes from the communist-era and from the Nazi occupation, the PAP said Sunday a team of forensic experts had come to that conclusion notably through handwriting analysis.

The 73-year-old former president and Nobel Peace laureate has been battling the allegations since last year, when the IPN seized previously unknown secret police files from the widow of a communist-era interior minister.

The IPN has said the files include a collaboration agreement signed with “Lech Walesa” and his alleged codename “Bolek”.

Walesa, who co-founded the independent Solidarity union and then negotiated a bloodless end to communism in Poland in 1989, has repeatedly denied the authenticity of the documents and once again called the accusations a “lie” on Saturday.

He enigmatically admitted however last year to having “made a mistake” and in the past had said he signed “a paper” for the secret police during one of his many interrogations.

A book published by the IPN in 2008 alleged that while the regime registered Walesa as a secret agent in December 1970, he was cut loose in June 1976 due to his “unwillingness to cooperate”.

Poles have mixed feelings about Walesa. His boldness in standing up to the communist regime is still widely respected, but the combative and divisive tone of his later presidency earned him scorn in many quarters.