This has to be a hoax, so take this with a grain of salt the size of Everest. According to Gizmodo a file has been spied on the FBI Vault website where old documents are put for the public to peruse that is a report on the infamous 1947 crash in Roswell, New Mexico that some believe was a UFO crash. The government has long maintained the crash was a weather balloon.
The document in question is a memo by an FBI agent named Guy Hottel that was working the original case and recounts what a so-called "investigator for the Air Forces" told him about the crash. The Air Force investigators name is blacked out in the memo. The reminder of the memo is an interesting read and conspiracy theorists will be riled up for sure.
The memo goes on to say that the Air Force found a crashed saucer shaped flying machine about 50-feet in diameter and that the investigator believed that the high-powered military radar in the area interfered with the UFO's controlling mechanisms. This is a crazy document to turn up on the FBI website for sure. Check out the document here.