All he believes is that Bush caused, or rather let, 9/11 to happen though his own incompetence, and has benefited from it. He also might think that bush knew about 9/11 and let it happen, I'm not really clear on it. In his own words

I wrote in "The Cause of Death" that Bush was not responsible directly, that he didn't plan 9/11, but he and his definitely benefited from the end result of all those people dying."

You can find this statement on his official website, specifically the 9/7/05 news post.

Fair enough, but he's also said many times that decades down the line when documents become declassified, then we'll know the truth about Sep.11. His default point of view can be reached simply with mainstream news sources...