I'm going to be very guarded in what I am about to say. During my military service, I saw things - some through the official course of my duties - and some in an unofficial capacity, that reluctantly convinced me that extra terrestrial beings not only exist, but they are far more prevalent than we have been led to believe.
The military often launched what we called 'disinformation campaigns,' which are official communications, designed to confuse and conceal factual circumstance, through the release of intentionally false statements. It is almost always justified as a matter of national security.
Much of the advanced experimental aviation technology our government is testing, through its various sub contractors, is not of terrestrial origin.