As the world awaited the US Senate report on the CIA’s detention and interrogation programme under the George W Bush administration, there was very little introspection in Europe. As if European countries had nothing to do with what went on in the hunt for al-Qaida in the years after 9/11. In fact, many of America’s European allies were deeply involved in the CIA programme. And they have managed to stay very quiet about it. Could this change now?

Under President Bush the CIA used a web of European airports and bases for its extraordinary rendition flights, secretly transferring terror suspects across borders for interrogation. Some European states helped the CIA to carry out kidnappings. Others hosted CIA “black sites” – in effect, torture chambers – on their territory. The 600-page redacted summary of the 6,000-page report, published on Tuesday by the Senate intelligence committee, will no doubt be scrutinised to see what it may reveal of the continent’s involvement in these abuses.

In 2007 a special investigator for the Council of Europe, Dick Marty, concluded that there was “enough evidence to state” that American secret prisons existed in Poland and Romania. He added that the “illegal deportation of suspects by CIA kidnapping teams in Europe” amounted to “a massive and systematic violation of human rights”.

After 9/11 the CIA reached out to its European allies as it embarked on its detention and extraordinary rendition operation. The aim was to place detainees beyond the reach of law. The active participation of dozens of foreign governments made both the renditions and interrogations possible. How many in Europe will now be pressed to disclose the full extent of their involvement in these operations?

To this day the exact scale of European complicity remains unknown. This is because of the secrecy maintained for years by the US and its partner governments. Washington has never confirmed the location of secret CIA prisons, nor named the governments that cooperated, and nor indeed does the material just published. A decade on, there is still no public comprehensive account.

But some facts have been established, thanks to the work of NGOs, the media, the European parliament and the Council of Europe. It is striking that all those who have attempted to shed light on the subject have said that governments actively obstructed their efforts, for instance by classifying the issue as “state secrets”.

European countries failed to conduct effective investigations into the agencies and officials who facilitated the CIA’s work. Sweden is the only country to have paid compensation to victims of extraordinary renditions. Italy is the only country where officials have been convicted by a national court for their involvement in the CIA programme.

According to information compiled by Open Society Foundations, at least 54 governments cooperated with these CIA activities. Twenty-one of those are European, of which 17 were at the time members – or soon to become members – of the European Union.

In addition to the countries above, the list of European states that were complicit in CIA rendition flights and other unlawful activities includes Lithuania (there are strong indications that this country also had a “black site”), the UK, Germany, Spain, Portugal, Belgium, Denmark, Finland, Iceland, Austria, the Czech Republic, Greece, Cyprus, Croatia, Bosnia-Herzegovina and Albania.

One of the best-documented cases relates to the abduction, on the streets of Milan in 2003, of Abu Omar, an Egyptian cleric who had been granted asylum in Italy. The CIA then secretly transported him to Egypt. In November 2009, in a case unique in Europe, an Italian court convicted 22 CIA agents, one US military official and two Italian intelligence operatives to at least five years imprisonment for their role in the kidnapping. The CIA agents were convicted in absentia and never extradited.

In 2004 Khaled El-Masri, a German citizen, was mistakenly seized in Macedonia and shipped by the CIA to Afghanistan, where he was detained. In 2012 this abduction and detention was condemned by the European court of human rights. But German authorities have always denied ever turning over information on El-Masri to the US.

Two Egyptians seeking asylum in Sweden, Ahmed Agiza and Muhammed al-Zery, were secretly apprehended by police in December 2001 and handed over to the CIA – who forcibly administered sedatives to them before flying them to Egypt, where they were tortured on an electric bed frame. After an investigation, in 2008 the two Egyptians were awarded $500,000 each in compensation.

These cases are some of the few that have led to lawsuits or official inquiries. In other instances, governments have managed to shroud almost everything in secrecy.

According to the 2007 Council of Europe report, Poland’s CIA “black site” was located at the Stare Kiejkury military training facility, and used by the CIA to torture “high-value detainees” – some of them Saudi, Yemeni and Algerian nationals. One was subjected by American interrogators to mock executions with a power drill as he stood naked and hooded. Poland’s judicial system and government officials have failed to shed light on any of this.

The UK cooperated closely with the CIA on detention and rendition – as documents found in Libya after the overthrow of Muammar Gaddafi in 2011 showed. But there have been few judicial cases or investigations.

European states that took part in the CIA operation were complicit in violating fundamental human rights, the Geneva conventions and the UN convention against torture. None, with the exception of Sweden perhaps, has admitted to any wrongdoing. Yet the strength of democracies resides precisely in their ability to recognise and debate their mistakes. In authoritarian countries where torture abounds, there is no such thing as public accountability.

As the US embarks on a renewed effort to get to the truth, this could be a good time for Europe to come clean. The bottom line is that fully exposing such practices is the only way to ensure they will never be repeated.