WARSAW, Poland (AP) — Prosecutors of Poland's historical institute are investigating the authenticity of documents the institute has released that purport to show that Solidarity founder Lech Walesa collaborated with the communist regime in the 1970s for money, the institute's head said Thursday.

Walesa, 72, former president, the founder of the Solidarity freedom movement that helped topple communism in 1989 and a Nobel Peace Prize laureate, denies he informed the security police on anyone and denies he ever took money from them. He says the documents are forged.

Lukasz Kaminski, head of the National Remembrance Institute, said that based on Walesa's statement, special prosecutors have opened a probe into documents alleging that Walesa collaborated under the codename "Bolek." Among the documents are reports on worker discontent at the Gdansk shipyard, where Walesa worked, receipts for money signed "Bolek" and finally the discharge of Bolek in 1976, when he was no longer considered a valuable source.

Last week the institute seized the documents from the home of the last communist-era interior minister, the late Gen. Czeslaw Kiszczak, acting on a law that requires key historical document to be handed in. It rushed to make photocopies of the documents available to journalists and historians, before having them checked by graphologists or other experts who could say whether they were authentic.

Police are known to have fabricated documents during that time. If the investigation proves that all or some of the documents were fabricated or forged, the authors could face prosecution.