European Union investigators, probing the alleged CIA abduction of a Kuwaiti-born German, on Saturday visited a hotel where he stayed in Macedonia in 2004.
"Why was he here for 23 days? And was he here voluntarily, or detained?" asked Mr Claudio Fava, who heads the committee in the European parliament investigating allegations of secret prisoner transfers and illegal detentions by the CIA in Europe.
Human rights groups cite the case of Mr Khaled el-Masri as an example of U.S. "extraordinary rendition" -- or secret transfers of terrorist suspects to third countries where they face abuse or torture.
The hotel visit ended a three-day trip to Macedonia by the investigative team of the European parliament.
Mr Fava told Reuters the investigators wanted to know who had paid Masri's bill at the hotel, where he said for the first 23 days of 2004.
"Somebody paid the bill," Mr Fava said in the foyer of the Skopski Merak hotel in a leafy district of the capital, Skopje. "But this is my question: Who paid?"
Mr Fava said on Friday there was no "hard evidence" to confirm Mr Masri's claim he was kidnapped by Macedonian agents before being flown by the CIA to Afghanistan for interrogation.
Mr Masri says he was pulled from a bus and detained on the Macedonian border on New Year's Eve 2003.
He told investigators he was held by Macedonian guards in a hotel and flown by the CIA to Afghanistan, where he was jailed as a terrorism suspect before being dumped without explanation in May 2004 in Albania.
Macedonia, pursuing EU accession talks and a US military ally in Iraq, denies any wrongdoing. It has acknowledged holding Masri at the border, but says he was released a few hours later.
Interior Minister Ljubomir Mihailovski said on Friday Mr Masri had exited at the main border crossing with Kosovo, Serbia's U.N.-run southern province. He described claims he left by plane as "pure speculation".
But the investigators point to a stamp in Mr Masri's passport from Skopje airport dated January 23, 2004, the day his lawyer alleges he was flown to Kabul via Baghdad and subjected to months of torture. Mr Masri is suing former CIA chief George Tenet.
"It's a little bit strange that a jobless guy came from Germany by bus, without a lot of money in his pocket, to close himself voluntarily in this room and then he paid by cash some 2,000 euros (1,374 pounds) for an expensive room," said Mr Fava.
Washington has declined public comment on the case.