The interim conclusions of his six-month investigation are that some 14 countries actively participated with the CIA operations, or turned a blind eye.
But this, he said, is only "part of the truth."
"I believe there is a dynamic now of the truth emerging to the surface," Marty told reporters. "And as we discover more elements, more people become willing to speak...and it allows me to affirm today that we certainly have not yet concluded our research."
Specifically, Marty said seven countries, including Macedonia, allowed CIA to seize suspects on their soil. That makes them responsible, he says, for a violation of the suspects' human rights.
Marty also said evidence pointed to secret detention centers having existed in Romania and Poland, despite denials from both countries.
He accuses other countries -- Cyprus, Germany, Spain, and Turkey -- of acting as "staging posts" for rendition operations. Another group of states -- Britain, Greece, Ireland, and Portugal -- stands accused of allowing "stopovers" by CIA planes carrying abducted suspects.
Marty's report does not, however, offer concrete proof. It relied primarily on flight logs to build up a picture of what he calls a "rendition circuit" around which suspects were transferred.
Still, in the case of the alleged CIA prisons, he said there are strong enough indications that they did exist. He was "not very surprised" to reach that conclusion, as an European Parliament investigation "points in the same direction."
It is now for the countries in question, he said, to investigate.
Kathalijne Buitenweg, a Dutch member of a European Parliament committee looking into the same allegations, said it is "very likely, and in some cases we have also proof," that several European countries have breached the continent's human rights conventions.
She called on them to come forward, saying that their continued silence makes them "passively guilty, which is in breach of the human rights convention."
Poland's reaction has been to dismiss the accusations as "slanderous." Prime Minister Kazimierz Marcinkiewicz said the report's claims were "not based on any facts."
It is not clear how -- or if -- the United States will respond to the report.
In the past, Washington has defended the practice of extraordinary rendition. In December, U.S. Secretary of State Condoleezza Rice declared that "the United States does not transport and has not transported detainees from one country to another for the purpose of interrogation using torture."
"The United States does not use the air space or the airports of any country for the purpose of transporting a detainee to a country where he or she will be tortured," Rice said. "The United States has not transported anyone and will not transport anyone to a country when we believe he will be tortured."
Marty's report will be debated on June 27 at the Council of Europe's Parliamentary Assembly, but the controversy looks unlikely to end there. And if -- as Marty predicts -- fresh revelations are forthcoming, other countries may yet be implicated.