Reporters of Polish Television and the Rzeczpospolita daily said the evidence included documents and witness statements that were part of a Polish judicial investigation to determine whether the alleged CIA prison undermined the country's sovereignty, the EUobserver reported Wednesday.
The journalists said the Polish government in December 2001 reportedly leased a section of the Stare Kiejkuty military base in northwest Poland to the CIA, and assigned 20 secret agents to assist U.S. officials in anti-terrorist activities.
U.S. planes began secret flights to the Szymany airport close to the military base in December 2002 and at least five planes landed in Szymany in 2003.
A witness giving evidence to the Polish investigation reportedly said in 2003 he spotted people, handcuffed and blindfolded, being led from a plane.
In previous years, the European Commission and the Council of Europe accused Poland of collusion but found no hard evidence to sanction alleged human rights violations, EUobserver said.