There's overwhelming evidence that Binladen and Zawahiri planned and executed the attack.

I wouldn't say the evidence was overwhelming. The only direct evidence I've found is:-

the two referred to "an incident that would take place in America on, or around, September 11" and they discussed potential repercussions. In another conversation with an associate in Afghanistan, bin Laden discussed the "scale and effects of a forthcoming operation." These conversations did not specifically mention the World Trade Center or Pentagon, or other specifics

I'm happy to be more overwhelmed if you have links.