The mother of all conspiracy theories over the years has been the JFK assassination. I’d guess that between Roswell and JFK, it would be a toss up on all of the books, movies, and conspiracy arguments.
Many found the Warren Commission report to be incomplete at best. When a plethora of documents were “sealed” the theories just went viral.
We’re coming up on the end of the waiting. 3000+ never seen documents and over 30,000 partially released documents from the FBI, CIA and Department of Justice are set to be released.
The CIA is calling for delaying the release for another 25 years. The very fact that they want to delay it should be the argument for releasing them. Read more here.