The FBI has joined an investigation by the U.S. Air Force over a crash near classified Area 51 after officials say someone tampered with the site.

The 432nd Wing, stationed at Creech Air Force Base in Clark County, said one of its aircraft was involved in an “incident” on September 23. The crash had no fatalities or injuries. The initial crash did prompt the closing of airspace over the base for a few days, due to “national security concerns.”

The site was secured and cleaned up quickly. However, on October 3, the base issued a statement that returning investigators discovered signs of “tampering” at the location, “including the presence of an inert training bomb body and an aircraft panel of unknown origin that were placed on the site post-incident.” The announcement caused some speculation online, considering the base’s history with rumored alien crashes.

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