Bob Lazar
I have always been intrigued by Bob Lazar to initial and most noteworthy whistle-blower regarding Area 51. This facility was established in the late 1940s or early 1950s but not officially recognized by the government until 2017 after over 60 years of operations. While I find Mr. Lazar credible, I understand the need for the operation at S-4 to be highly classified (and think his actions were likely in violation of his NDA). Some reports indicate that anything to do with alleged ET crashes is in a “special” security classification of “Above Top Secret”. I suspect that several other countries (both allies and foes) also have similar operations. Since any new technology will likely have military applications, we should guard what we learn jealously and we do. So far it seems that reverse engineering has been extremely challenging. Keep in mind that the technology could be thousands of years ahead of our current understanding. It might be like a person from the Dark Ages attempting to reserve engineer a space shuttle.
There are dozens of videos available that do a decent job of telling the story. The following one is from early on when Bob was still a young man.
Here is a more recent one: https://www.youtube.com/watch?v=-jxJ0vO9uHc