In the few months preceeding the Sept.11 attacks there was a significant amount of military buildup and increased tensions in the Caspian Sea over how the undersea oil fields were to be divided up. Russia was the first to move its navy into the area. The other countries then began a buildup of their own, with Iran being the first to show a willingness to show open hostility and acts to secure it's share of the Caspian Oil reserves. Prior to this Iran had been actively acquiring large quantities of conventional weapons and a full assortment of weapons of mass destruction directly from Russia, including biological and chemical weapons. At the same time it had ignored profitable gas pipeline deals with Turkmenistan and instead showed preference for China building a pipeline through Afghanistan. They did this because China is a primary member of the international economic organization (I forget the title???). For years there was basically an impasse over who was going to build the pipeline and where it was going to go. Meanwhile Afghanistan was suffering from a post-Soviet civil war that had lasted 12 years because surrounding countries kept supplying both sides with arms - Pakistan supplied the Taliban while Iran, Russia, et al supplied the northern alliance).

Anyways it looks like there was a very substantial military buildup in the region just a few months before the attacks on the World Trade Centre in New York. I spent hours reading these articles in chronological order - it is impossible to ignore the connection to Caspian Sea Oil reserves:

Radio Free Europe:
http://www.rferl.org/

Energy Politics in the Caspian:
http://www.rferl.org/nca/special/caspian/