Lawyers for two men who say they were held illegally in a secret CIA jail on Polish territory argue that a landmark criminal investigation into the "black site" is being stalled because a trial will embarrass the Polish state.
Polish prosecutors are investigating the country's role in a global operation run by US secret services a decade ago to transport suspected al Qaeda members to facilities outside the United States where they could be held and interrogated without the safeguards set out under US law.
Poland is one of only two countries known to have opened a criminal investigation into the secret jails, and its case could set a precedent for prosecutions in other countries. If it languishes, it greatly reduces the chances that the global veil over "black sites" will be lifted.
What little information has emerged suggests the case could implicate some of Poland's most senior politicians in illegal detentions and upset the United States, a key ally.
Lawyers, human rights activists and other sources familiar with the case say that what started out as a robust investigation appears to have ground to a halt since the original investigators were taken off the case early last year.
"The image is of a complete lack of action," said Mikolaj Pietrzak, lawyer for Saudi national Abd al-Rahim al-Nashiri, who says he was detained in a CIA jail on Polish soil.
"The case is obviously, in my opinion, under political control ... The most convenient thing politically is for the case to drag on," said Pietrzak.
Polish officials say the prosecutors are independent, while the prosecutors say they are doing all they can to collect evidence, arguing that their work had been slowed in part because US officials had not responded to requests for information.
A spokesman for the US embassy in Warsaw declined comment on the case because, he said, it concerned intelligence issues.
Former US President George W. Bush said in 2006 that the CIA operated detention facilities outside US territory, but Washington has not detailed where they were or how they worked.
The Polish investigation, already in its fifth year, is due to end next month and prosecutors say they may apply to extend it. If they do not, the case would have to be brought to trial or closed, both politically risky options for Poland.
The problem, said Jozef Pinior, a Polish senator who has lobbied for a full investigation into what the CIA was doing in Poland, is that security officials from the time of the alleged CIA operations exert influence through an "old boys' network".
"They (the government) are in a sandwich between opening this issue up and the pressure from the hard core of the Polish state, the secret service, the prosecutor's office, who say: 'Let's keep this secret'," said Pinior.
The only other country to open a criminal investigation into allegations of CIA jails on its soil was ex-Soviet Lithuania, but that case is no longer open.
Poland's government, a centrist coalition with close ties to Washington, was not in office when the alleged CIA "black site" was in operation. It has said it wants a full investigation.
Prime Minister Donald Tusk's office, in response to Reuters questions about the case, said that prosecutors' independence was established by law. "No executive body can influence the prosecutor's actions," it said in a statement.
According to documents filed by lawyers for the two men who say they were held by the CIA in Poland, detainees were flown to the tiny Szymany airport and then driven to a lakeside Polish intelligence academy in the village of Stare Kiejkuty, about 180 km (110 miles) north of Warsaw, where the CIA had a facility.
Polish officials have never publicly acknowledged the existence of CIA prisons in Poland.