Federal prosecutors believe the Turkish-German, named as Kadir T., allegedly supported the four-member Sauerland cell by purchasing a video camera and night-vision goggles in June 2007 for the Islamic Jihad Union (IJU) in Pakistan. Cell member Adem Yilmaz is thought to have worked with the extremist group, which has been linked to al-Qaida.
Yilmaz allegedly used his brother Burhan Yilmaz to hand over the items, the Karlsruhe-based federal prosecutors said.
According to daily Frankfurter Allgemeine Zeitung on Friday, Kadir T. was travelling to the Afghan-Pakistan border to attend a terrorist training camp when he was arrested on Thursday.
The Sauerland cell is currently on trial after being arrested in September 2007 for planning attacks on Americans in Germany.
Earlier this month 29-year-old mastermind and German Islam convert Fritz Gelowicz admitted in court that he and the three other defendants had aimed to kill as many US soldiers based in Germany as possible. The planned attack was meant to warn Germany to remove its troops from Afghanistan.