The mystery surrounding the supposed UFO crash outside of Roswell, N.M., on July 7, 1947, has been enticing enough to sustain decades of alien conspiracy theories, jokes, a Google Doodle and even a steamy teen romance TV show. Sixty-six years later, despite the official story attributing the debris recovered to a weather balloon, many still cling to visions of flying saucers and alien autopsies.

In support of the alien theory, Roswell researchers have collected witness testimonies from those who supposedly saw the debris or the remains of the extraterrestrials. But skeptics point out that many of these recollections are second- or third-hand, and sometimes recalled decades after the 1947 crash.

What's the official explanation? An Air Force report prepared in the 1990s concluded that the debris collected near Roswell most likely came from Project Mogul, a then-top secret project aimed at detecting Soviet atomic bomb tests. Other elements of the alien spacecraft story, the military says, are cherry-picked from other incidents.

“Air Force activities which occurred over a period of many years have been consolidated and are now represented to have occurred in two or three days in July 1947,” the USAF said.

Reports of alien “bodies” likely stem from sightings of the human-shaped test dummies that the USAF attached to high-altitude balloons (like the ones used in Project Mogul) for scientific research, according to the military. There also were aircraft and balloon accidents near Roswell in the 1950s that may have contributed to reports of alien bodies housed at the airfield’s hospital.

Test dummies were sometimes dropped from balloons during military experiments. US Air Force

In 1995, the U.S. General Accounting Office – the Congressional “watchdog” agency that keeps tabs on how taxpayer dollars are spent – released a follow-up report focused on finding any additional records on the incident outside of those in the Air Force report. The GAO found two pieces of evidence from 1947 – a history report from the Roswell Army Air Field (RAAF) and its 509th Bomb Group, and an FBI teletype message from July 8, 1947 – the day after the crash.

The Army report mentioned that the 509th recovered “a ‘flying disc’ that was later determined by military officials to be a radar-tracking balloon,” the GAO wrote. The FBI message, meanwhile, relayed that the military had recovered “an object resembling a high-altitude weather balloon.”

However, there are still some large gaps in the historical record that can still prove fodder for the imagination. The GAO noted that the RAAF’s administrative records and outgoing messages over a space of several years (from a year or two before the crash to a couple of years afterward) had been destroyed.

The paper trail “does not indicate what organization or person destroyed the records and when or under what authority the records were destroyed,” the GAO wrote.

Administrative mix-up? Or the work of some nefarious Men in Black?

Alien visitors aren’t even the wildest theory floating around the Roswell incident. Journalist Annie Jacobsen’s 2011 book “Area 51: An Uncensored History of America’s Top Secret Military Base” (the material recovered at Roswell was supposedly spirited away to Area 51 in Nevada) includes a chapter airing the claim that the Roswell crash was really a Soviet spy plane piloted by children surgically altered by the infamous Nazi doctor Josef Mengele. The plan was, apparently, to scare American citizens.