There's plenty work done on crash retrievals etc by many researchers. There's one case before Roswell that's really considered even more as facts than Roswell by the researcher Richard Dolan. It kind of depends of what understanding you have of the events being facts and fiction. Which has nothing to do with aliens or such per say. So for over 70 years there's been a structural coverup of either the retreivals of crash ships or unknown objects in very strict airapace, this is done by the so called "cabal". The reason is because it's such delicate technology either retrived or in our airspace that the absolute silence will "fool" the public and other nations to not dive into the subject. It's obvious that these object does not use our conventional means of travel or fuel. To release any data leading to the Disclosure of the coverup would collapse our social, industrial and political structure. This is not some villain who sits in his lair pushing buttons. It's a group of people with close to infinite amount of money who will do anything to get their way. Most people cannot take it all in unless you've had some experience with the subject. So if you're not experienced I suggest you to listen to some of the very renowned researchers like Timothy Good, George Knapp, Stanton Friedman, Richard Dolan etc. Have fun thanks for reading.