I'm not sure that he proves his argument, but he makes a very convincing argument that the CIA's involvement was largely to obtain false confessions that linked Al Qaeda to 9/11.
Let’s be clear: the Senate Committee [report]...states that the CIA did not question the detainees, but it conditioned them to confess to acts of which they knew nothing. The Commission states that the CIA agents did not even look to see what the detainees had confessed during previous interrogations with the authorities who arrested them. In other words not only has the CIA not investigated whether al Qaeda was involved in the attacks or not, but its action had no other purpose than to generate false evidence attesting to the involvement of al-Qaeda in the attacks of September 11.Considering that 9/11 critics have assembled considerable evidence implicating the CIA in the 9/11 attacks to justify the US invasion of Afghanistan and Iraq and the whole "war on terror" to justify the construction of many elements of a police state domestically, such CIA actions in relation to these prisoners as argued by Meyssan make perfect sense. The link between 9/11 and Al Qaeda, which was alleged by government officials immediately after 9/11, had to be firmly established by these pseudo confessions to complete the false flag scenario concocted by the CIA.