Here is some info on the Sauerland cell of 2007 (unfortunately in German):

http://www.stern.de/panorama/sauerland-zelle-mutmasslicher-c...

Quick summary: The person the people in the Sauerland cell called "boss" and who organised the fuses for them was a "contact person" for MİT (Turkish intelligence org.) and CIA.

https://en.wikipedia.org/wiki/National_Intelligence_Organiza...

Background:

https://en.wikipedia.org/wiki/2007_bomb_plot_in_Germany