"Some" claim Bin Laden isn't real or not responsible for 9/11 - If true, why hasn't anyone proven this?

I'm not looking to spark an argument where everyone throws unproven conspiracy theories at me or talks about the velocity of the alleged missle that hit the pentagon and how it wasn't a plane etc....I'm looking to get opinion on why Bin Laden, Al Qaeda, US Government Insiders, Other Governments, Wealthy People of Influence etc. have not come out & said "this is a cover up" - That of course, is if it is a cover up. My personal opinion is that a) Bin Laden is real b) He was involved and c) There is some sort of cover up, but its not as big as "The US did it" or "Bin Laden isn't real" etc. --- Love to hear some opinions, especially with facts or quotes from people who are in a position to know!!! In this day and age, how could we all be fooled? This isn't the 60s.