UFO Crash Coverups. One common UFO conspiracy theory, including the one proposed by Grusch, is that the government is hiding remnants of a UFO that crashed into the Earth. One of the first crash coverup conspiracies began in 1947 in Roswell, New Mexico, when reports of debris from a flying saucer were discovered near a military base.

​https://www.discovermagazine.com/the-sciences/fact-or-fiction-what-is-the-truth-behind-alien-conspiracy-theories