There is actually an extensive documentary that goes into very specific detail about how 9/11 might have been faked to give justification to one of the most unpopular wars to ever take place in modern history. AKA the Iraq War.
It still baffles me that we went to war with Iraq when it was supposedly Afghanistan that was harboring Bin Laden, further proving that something was DEEPLY wrong.
The Afghanistan war was already 2 years old when we entered Iraq. We started bombing Afghanistan almost immediately after 9/11. The reason, at the time, for entering Iraq was a combination of removing a tyrant (Sadamm) who gassed his own people, and potential WMD's in Iraq. Don't get me wrong, killing him was not a bad thing. He was a monster. However lying to the American public about WMD's when it was clearly about oil was BS from the start.
As far as an inside job, i dont think so. While the CIA did train Bin Laden and other terrorist cells, it was to help them combat the Russians during the heat of the Cold War. Then those same terrorists took all the training we gave them and sent it right back once we became the new enemy after the fall of the Soviet Union. So in essence, we did train the guys who carried out the attack, but we didnt plan or specifically know about the attack.