Federal prosecutors told a court in the western city of Koblenz that 37-year-old Ahmad Wali Siddiqui wanted to carry out terrorist acts in Germany and elsewhere, German news agency dapd reported.
Siddiqui was captured by U.S. troops in Afghanistan in July 2010 and while in custody provided details on alleged al-Qaida plots supposedly targeting European cities, prompting Germany to raise its terror alert to the highest level since the days of the extreme-left Red Army Faction. The RAF was disbanded in the late 1990s.
Authorities have said Siddiqui was one of about a dozen radical Muslims who left the northern German city of Hamburg in 2009 to pursue terrorist training in the lawless border region of Pakistan and Afghanistan.
Another member of the group, German-Syrian dual national Rami Makanesi, was convicted last year in a Frankfurt state court of membership in al-Qaida and sentenced to four years and nine months. He was arrested in Pakistan in June 2010 and then extradited to Germany.
Prosecutors Bernd Steudl told the court Monday there was "no doubt" Siddiqui first joined the Islamic Movement of Uzbekistan and then al-Qaida, and that he had wanted to participate in a "jihad," or holy war.
Siddiqui told the court that he merely repaired computers, played basketball and cured a knee problem during his trip to Pakistan.
Senior prosecutors Ulrich Schultheis dismissed that account.
"Al-Qaida isn't sanatorium for deadbeats," he was quoted as saying by dapd.
Intelligence officials have previously said Siddiqui was a friend of Mounir el Motassadeq, who was convicted by a German court in 2006 of being an accessory to the murder of the 246 passengers and crew on the four jetliners used in the Sept. 11 terrorist attacks. They both frequented a now-shuttered mosque in Hamburg.
The trial is expected to last several more days.