There are a growing number of theories in circulation about the Habbush forgery revealed in Ron Suskind's The Way of the World. The forgery was publicized in December 2003 - 6 months after the invasion, when it became clear no WMD's were found going to be - in an attempt to prove there were pre-war ties between Saddam Hussein and Al Qaeda.

I'll try to keep track of them here... 

CIA officials Rob Richer and John Maguire

• Ron Suskind: under direct orders coming from CIA Director George Tenet 

CIA asset and former Iraq Intelligence Chief Habbush

• Juan Cole: Habbush forged the letter himself and the CIA "authenticated" it in bad faith through its asset Ayad Allawi--whom journalist Con Coughlin contacted to vouchsafe the letter's authenticity after it was leaked to him.

Doug Feith’s Office of Special Plans

• Philip Giraldi: My source also notes that Dick Cheney, who was behind the forgery, hated and mistrusted the Agency and would not have used it for such a sensitive assignment.  Instead, he went to Doug Feith’s Office of Special Plans and asked them to do the job.  The Pentagon has its own false documents center, primarily used to produce fake papers for Delta Force and other special ops officers traveling under cover as businessmen.  It was Feith’s office that produced the letter and then surfaced it to the media in Iraq.  Unlike the Agency, the Pentagon had no restrictions on it regarding the production of false information to mislead the public.  Indeed, one might argue that Doug Feith’s office specialized in such activity.