The government clearly knows more than they admit. They clearly stated this when the Air Force summarized Project Blue Book, admitting openly that even after the most extravagant and ludicrous "explanations" to cover what they could, a significant portion of the sighting still could not be explained.
There will always the post-Roswell questions concerning access to alien technology. For that matter, Roswell has always left more questions than any of the ridiculous answers offered by the government, and it always will.
My personal opinion is that Area 51 arose from this as the perfect and beautifully executed cover-up for whatever is really going on elsewhere. Area 51 has kept America's attention firmly focused in one specific area since it's inception - no one is really looking anywhere else.
Many years ago I had an interesting an unusual experience that clearly defined the government's insanity as well as it's efforts to hide things.
While living in Colorado Springs, I heard a loud roaring engine sound approaching my house while I was photographing our new back yard. I turned and started snapping pics just in time to see a huge, strange aircraft roar low directly overhead, an aircraft I was able to identify as an SR-71, presumably taking off from nearby Peterson Airbase.
Being both a concerned citizen and one fully aware of air restrictions over populated areas, I immediately called the duty officer at Peterson and told him what I saw, adding that the aircraft was well below FAA limits for traveling over a city suburb - roughly 200 feet or less and moving at full throttle - probably didn't dare use 'burners that low over houses.
I was, of course, informed that no such aircraft had left Peterson, nor was such an aircraft anywhere in this Colorado area. "Fine", I responded. "I guess I'll just submit my photos for civilian analysis."
A short - very short - while later, some serious people form Pete Field showed up demanding my photos. "What photos?" I replied. According to the duty officer at Pete Field, no such event occurred; therefore, there cannot be any photos of such an event for you to confiscate."
This was poorly received, and they demanded my film, so I gave them my roll of film. In fact, I gave them a blank roll of film, since they asked for "the film in my camera", which I had just swapped out for a fresh roll, anxious to get my shots developed. I always comply with official requests, to the letter.
When they returned the next day, accusing me of giving them the wrong film, I replied that I had given them what they requested, and as far as I was concerned, they had botched the development and that was not my problem.
One hell of an aircraft, though, especially from less than 200 feet overhead!