Some of the 19 hijackers were students here, including the men believed to have been at the controls of aircraft that crashed into the World Trade Center and the Pennsylvania countryside on 11 September.
Suspected hijackers Mohamed Atta, Marwan Al-Shehhi and Ziad Samir Jarrah lived in the same Hamburg apartment at various times while attending university in the 1990s. They were allegedly members of a terrorist cell that was part of Osama Bin Laden's network, al-Qaeda, that operated in that city since at least 1999, according to US and German officials. It is believed that the attacks may have been planned from their flat on Marien Street.
Three men believed to have been accomplices - Said Bahaji, Ramzi Binalshibh and Zakariya Essaabar - are now wanted by German and US police. They are thought to have left the country shortly before 11 September. The FBI thinks Binalshibh may have been intending to take part in the attacks – the so-called 20th hijacker – but was denied a visa.
Questions are now being raised over how German authorities failed to see signs of the terrorist cell. Funding for Germany's intelligence system has been trimmed back since the fall of the Berlin Wall.