[LOOKAYANNER]

From what I've read and seen on TV about the incident, from both sides of the issue, what happened at Roswell was more than likely debris from a secret U.S. program called Project Mogul. This was during the times following WWII when the Cold War was as strong as ever between the U.S. and the Soviet Union. Mogul had to be kept top secret because it involved high altitude balloons meant to detect sound waves made by Soviet atomic bomb tests and ballistic missles. So everything had to be hush-hush. The aliens bodies were likely a combination of innocently transformed memories of the recovery of anthropomorphic dummies in military programs like Project High Dive. Some are simply misinformation from UFO proponents wanting to sell books and cash in on the Roswell incident. The effects of time on memories can cause confusion about when events happened and what happened. I mean, the Roswell Incident happened in 1947, but there wasn't much interest in it until a National Enquirer article about it in 1978, over 30 years later. That's when everyone and his uncle began coming out with "stories" that they knew but hadn't revealed until the Enquirer article. And many of the "witnesses" have changed their stories numerous times and have been discredited.
You can bet your last dollar that if anyone had any credible evidence of a cover-up of aliens and spacecrafts, that it would have come out long before 1978. There's no way a secret like that could be kept.