How could they keep this a secret ? One example of the length's they will go to, is that when in office, President Jimmy Carter, requested information regarding evidence of the existence of extraterrestrials. He was denied access, being determined as a security risk by the then head of security George H Bush. The secret is maintained due to the compartmental nature of the Military industrial Complex. The left hand does not know what the right hand is doing. The witnesses are from the inside who were obliged to swear secrecy, but decided to speak when they decided the secret was one that no country or organization should hold to it's self.
There is more between heaven and earth than is dreamed of in our imaginations.