I go first:
I am convinced, and have no doubt, that 4 civilian airplanes were hijacked and intentionally flown into 3 buildings. One crashed near Shanksville.
I am convinced, and have no doubt, that all the physical damage and loss of life on that day were a result of the plane crashes and the fires they started. No bombs, no additional incendiaries, no controlled demolition
I am convinced, and have no doubt, that the hijackers commaded the cockpits and flew the planes. No remote control.
About flights 11, 175 and 77, I have nothing additional to say.
I am certain, but allow residual doubt, that flight 93 crashed because its passengers resisted and violently iterferred, thus making the hijacker-pilot lose control and crash. No shoot-down to be sure.
I am convinced, and have no doubt, that the hijackings caught FAA and the military units that were on alert to defend the airspace by surprise, that they did everything they could to handle the situation, but were unable to do anything about the 4 planes. The main reasons for this inability were: Too little time; no contingency plans for such situations, resources too thinly spread; inadequate sharing of information between civilian and military agencies due to inadequate or incompatible technology.
I am fairly certain that some agencies of the US goverment had in their possession information that, if assembled and interpreted lucidly ahead of time, might have enabled them to intervene and bust the terrorists before 9/11. I can't judge fairly if the failure to do so is due to avoidable incompetence, or if the odds of finding such information in a sea of data are just prohibitively slim. I do not believe that anyone in these agencies knew of the plan and consciously decided not to interfere. I allow for the remote possibility that there are nefarious elements in the agencies who might be so inclined.
I am certain that the hijackers were a group of 19 or 20 Arabs, mostly from Saudi-Arabia, who were recruited by Al Quaeda, had the blessing of OBL. Among their leaders were KSM and Mohammed Atta. I admit that there is a little wiggle room for doubt, as KSM was abducted in secrecy and tortured. I want to take information presented by secret services with a good grain of salt.
I believe the suicide terrorists were personally motivated mainly by a general feeling of hatred and powerlessness towards the USA and the secualar west. Grievances in connection with the situation in Palestine, and other middle-eastern issues may also individually have placed a role. They were mostly devout muslims of a radical provenance who believed the preaching that they will go to paradise if killed in action against non-believers.
I believe OBL and Al Quaeda hoped to lure the USA into a violent and costly reaction. Secondary goals may have been to gain prestige and attract recruits and other support from muslims around the world, position Al Quaeda as the leading islamist resistance group, or stir up popular uprisings in Arab lands against regimes that Al Quaeda opposes (the monarchies of Saudi-Arabia and Jordan for example, or the Israeli occupations).
I am satisfied with the forensic investigations. They were humongous tasks, had do dive deep into unknown territories, and by and large the efforts were carried out honestly, competently and with sufficient thoroughness. With hindsight, some minor weaknesses may be lamented, such as the failure to investigate WTC7 with the same diligence as WTC1 and 2 were. It is my understanding that the debris of the twin towers was investigated more thoroughly, which undoubtfully is due to its containing so many human remains. There is no foul play.
I think the 9/11 Commission did a great job.
I believe the government, and some agencies thereof, have been too hesitant to allow reviews of their roles in desaster management and preparedness.
I lament that no co-ordinated debate has taken place about the political implications and the fall-out of the attacks. 9/11 has been abused by the Bush administration to further unrelated and sweeping agendas to the detriment of the American people.