On April 4 1949 special agents sent a cable marked 'urgent' to the bureau director, Edgar Hoover.
The top secret document reveals how an army guard, a policeman and a highway patrol, who were all miles apart, each saw a UFO, which they said exploded over mountains near Logan, north of Salt Lake City.
© Ken Lund via WikipediaExtra-terrestrials? Secret documents reveals details of sightings of a UFO exploding over mountains at Sardine Canyon, north of Salt Lake City in Utah
The memo is one of thousands of previously unreleased classified files that the bureau has made public in a new online resource called The Vault.
Under the title 'Flying Discs', the document about the sightings in Utah said the three men each 'saw a silver coloured object high up approaching the mountains at Sardine Canyon' that 'appeared to explode in a rash of fire.'
It added: 'Several residents [reported] seeing what appeared to be two aerial explosions, followed by falling object.'
Documents show that an earlier UFO sighting had been investigated in Logan in September 1947.
It said numerous witnesses told the FBI they saw 'flying discs' in formation that were 'circling the city at a high rate of speed'.
Also among the files, released for the first time, is a memo from Guy Hottel, the special agent in charge of the Washington field office in 1950, which appears to prove that aliens landed at Roswell, New Mexico.
Proof of (alien) life? A copy of the 1950 memo that recounts the discovery of flying saucers and aliens in New Mexico. The memo has been published on the FBI website
In the memo, whose subject line is 'Flying Saucers', Agent Hottel reveals that an Air Force investigator had stated that 'three so-called flying saucers had been recovered in New Mexico'.
The investigator gave the information to a special agent, he said. The FBI has censored both the agent and the investigator's identity.
Agent Hottel went on to write: 'They were described as being circular in shape with raised centers, approximately 50 feet in diameter.
'Each one was occupied by three bodies of human shape but only 3 feet tall,' he stated.
The bodies were 'dressed in a metallic cloth of a very fine texture. Each body was bandaged in a manner similar to the blackout suits used by speed flyers and test pilots.'
Was it true? An image, later disproved a hoax, showing one of the aliens that were autopsied at Roswell in 1947
He said that the informant, whose identity was censored in the memo, claimed the saucers had been found in New Mexico 'due to the fact that the Government has a very high-powered radar set-up in that area and it is believed the radar interferes with the controlling mechanism of the saucers'.
He then stated that the special agent did not attempt to investigate further.
The release of the secret memo is likely to fuel conspiracy theorists' claims of a government cover-up.
The town of Roswell in New Mexico became infamous after reports that a flying saucer had crashed in the desert near a military base there on or around July 2, 1947.
The bodies of aliens were said to have been recovered and autopsied by the U.S. military, but American authorities allegedly covered the incident up
© FBIRoswell: Secret memo released online is written to the FBI Director and could confirm the 1947 Roswell UFO incident
Flying saucers: One of the faked photos of the supposed alien victims of the Roswell UFO crash
The headlines screamed: 'Flying Disc captured by Air Force.' Yet, just 24 hours later, the military changed their story and claimed the object they'd first thought was a 'flying disc' was a weather balloon that had crashed on a nearby ranch.
Amazingly, the media and the public accepted the explanation without question. Roswell disappeared from the news until the late Seventies, when some of the military involved began to speak out.
Another memo published in The Vault from 1947 claimed that an object 'purporting to be a flying disc' had been recovered near Roswell.
The disc was 'hexagonal in shape' and 'suspended from a balloon by a cable', according to the memo, marked as 'Urgent', to the FBI director.
Autopsy: A dead alien is allegedly examined following the landing at Roswell. The photo was later shown to be a hoax
The disc and balloon were being transported to Wright Field for further inspection, the memo noted.
It added that the information was being flagged up because of 'national interest' in the episode, and noting that both NBC and the AP were set to break the story that day.
Warning: Video contains graphic material
Roswell Alien Autopsy
what does this mean for us today? there are no weather ballons what you are seeing in the skys is real. So if they are real what else has the gov. been keeping from us in this regard.....the lies will always continue to pile up....