In northern Bucharest, in a busy residential neighborhood minutes from the center of Romania's capital city, is a secret that the Romanian government has tried for years to protect.
For years, the CIA used a government building - its code name Bright Light - as a makeshift prison for its most valuable detainees.
There, it held al Qaeda operatives Khalid Sheik Mohammad, the mastermind of 9/11, and others in a basement prison before they were ultimately transferred to Guantanamo Bay in 2006, according to former U.S. intelligence officials familiar with the location and inner workings of the prison.
The existence of a CIA prison in Romania has been widely reported, but its location has never been made public until a joint investigation by the Associated Press and German public television, ARD Panorama.
The news organizations located the former prison and learned details of the facility, where harsh interrogation tactics were used.
The Romanian prison was part of a network of so-called black sites that the CIA operated and controlled overseas in Thailand, Lithuania and Poland. All the prisons were closed by May 2006, and the CIA's detention and interrogation program ended in 2009.
Unlike the CIA's facility in Lithuania's countryside or the one hidden in a Polish military installation, the CIA's prison in Romania was not in a remote location. It was hidden in plain sight, a couple of blocks off a major boulevard on a street lined with trees and homes, along busy train tracks.
The building is used as the National Registry Office for Classified Information, which also is known as ORNISS. Classified information from NATO and the European Union is stored there.
In an interview at the building in November, senior ORNISS official Adrian Camarasan said the basement is one of the most secure rooms in all of Romania. But he said Americans never ran a prison there.
"No, no. Impossible, impossible," he said in an ARD interview for its "Panorama" news broadcast, as a security official monitored the interview.
Shuttling detainees into the facility without being seen was relatively easy. After flying into Bucharest, the detainees were brought to the site in vans. CIA operatives then drove down a side road and entered the compound through a rear gate that led to the actual prison.
The detainees then could be unloaded and whisked into the ground floor of the prison and into the basement.
The basement consisted of six prefabricated cells, each with a clock and arrow pointing to Mecca, the officials said. The cells were on springs, keeping them slightly off balance and causing disorientation among some detainees.
The CIA declined to comment on the prison.