Why is Osama wanted for bombings in Tanzania but not for 9-11?

The FBI's wanted page says he's wanted for the 1998 bombings of an emby in Tanzania but doesn't mention anything about 9-11. Why did they give the impression he was ociated with 9-11 when he's never admitted it and why are we in Afghanistan post 9-11 looking for him there when he has nothing to do with 9-11? Why wasn't he wanted 1998-2001 and now there's a $25 mil reward for his capture post 9-11 yet he's not charged for 9-11?