Saudi Arabia
Major Events > 9-11 Crimes > Foreign Governments
An entire book could be written about the role that the Saudis played in the 9-11 incident. I won't have the time to write such a book but I will point out some key issues as to why these guys are in to this crime up to their chins.
Update June 2015
Here is a good report on the status of the 9-11 families efforts to free up data against the Saudi involvement in supporting the terrorists.