Sixty years ago, a light aircraft was flying over the Cascade Mountains in Washington state, at a height of around 10,000 feet.
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Suddenly, a brilliant flash of light illuminated the aircraft.
Visibility was good, and as pilot Kenneth Arnold scanned the sky to find the source of the light, he saw a group of nine shiny metallic objects flying information.
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He estimated their speed as being around 1,600 mph — nearly three times faster than the top speed of any jet aircraft at the time.
Soon, similar reports began to come in from all over America.
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This wasn't just the world's first UFO sighting — this was the birth of a phenomenon, one that still exercises an extraordinary fascination.
Military authorities issued a press release, which began: "The many rumors regarding the flying disc became a reality yesterday when the intelligence officer of the 509th Bomb Group of the Eighth Air Force, Roswell Army Air Field, was fortunate enough to gain possession of a disc."
The headlines screamed: "Flying Disc captured by Air Force".
Yet, just 24 hours later, the military changed its story and claimed the object it had first thought was a "flying disc" was a weather balloon that had crashed on a nearby ranch.
The key witness was U.S. Army Maj. Jesse Marcel, the intelligence officer who had gone to the ranch to recover the wreckage.
He described the metal as being wafer-thin but incredibly tough.
It was as light as balsa wood, but couldn't be cut or burned.
These and similar accounts of the incident have largely been dismissed by all except the most dedicated believers.
Astonishing new twist
But last week came an astonishing new twist to the Roswell mystery.
Lt. Walter Haut was the public-relations officer at the base in 1947 and was the man who issued the original and subsequent press releases after the crash on the orders of the base commander, Col. William Blanchard.
Haut died in December 2005, but left a sworn affidavit to be opened only after his death.
Last week, the text was released. It asserts that the weather-balloon claim was a cover story and that the real object had been recovered by the military and stored in a hangar.
He described seeing not just the craft, but alien bodies.
He wasn't the first Roswell witness to talk about alien bodies.
Local undertaker Glenn Dennis had long claimed that he was contacted by authorities at Roswell shortly after the crash and asked to provide a number of child-sized coffins.
When he arrived at the base, he was apparently told by a nurse (who later disappeared) that a UFO had crashed and that small humanoid extraterrestrials had been recovered.
But Haut is the only one of the original participants to claim to have seen alien bodies.
UFO pieces handed around
Haut's affidavit talks about a high-level meeting he attended with base commander Col. William Blanchard and the Commander of the Eighth Army Air Force, Gen. Roger Ramey.
Haut states that at this meeting, pieces of wreckage were handed around for participants to touch, with nobody able to identify the material.
He says the press release was issued because locals were already aware of the crash site, but in fact there had been a second crash site, where more debris from the craft had fallen.
The plan was that an announcement acknowledging the first site, which had been discovered by a farmer, would divert attention from the second and more important location.
The clean-up operation
Haut also spoke about a clean-up operation, where for months afterward military personnel scoured both crash sites searching for all remaining pieces of debris, removing them and erasing all signs that anything unusual had occurred.
This ties in with claims made by locals that debris collected as souvenirs was seized by the military.
Haut then tells how Colonel Blanchard took him to "Building 84" — one of the hangars at Roswell — and showed him the craft itself.
He describes a metallic egg-shaped object around 12-15 feet in length and around 6 feet wide.
He said he saw no windows, wings, tail, landing gear or any other feature.
Haut "saw the alien bodies"
He saw two bodies on the floor, partially covered by a tarpaulin.
They are described in his statement as about 4 feet tall, with disproportionately large heads.
Towards the end of the affidavit, Haut concludes: "I am convinced that what I personally observed was some kind of craft and its crew from outer space."
What's particularly interesting about Walter Haut is that in the many interviews he gave before his death, he played down his role and made no such claims.
Had he been seeking publicity, he would surely have spoken about the craft and the bodies.
Did he fear ridicule, or was the affidavit a sort of deathbed confession from someone who had been part of a cover-up, but who had stayed loyal to the end?
The U.S. government came under huge pressure on Roswell in the '90s.
In July 1994, in response to an inquiry from the General Accounting Office, the office of the secretary of the Air Force published a report, "The Roswell Report: Fact Versus Fiction in the New Mexico Desert."
Weather balloon "cover story"
The report concluded that the Roswell incident had been attributable to something called Project Mogul, a top-secret project using high-altitude balloons to carry sensor equipment into the upper atmosphere, listening for evidence of Soviet nuclear tests.
The statements concerning a crashed weather balloon had been a cover story, they admitted, but not to hide the truth about extraterrestrials.
A second U.S. Air Force report concluded that the claims bodies were recovered were generated by people who had seen crash-test dummies dropped from the balloons.
Skeptics, of course, will dismiss the testimony left by Haut.
After all, fascinating though it is, it's just a story. There's no proof.
But if nothing else, this latest revelation shows that, 60 years on, this mystery endures.