Probably the most debated extra-terrestrial event happened today in 1947 when either a UFO or a weather balloon crash-landed on a farm near Roswell Air Base.
A rather large group of people believe that the 'weather balloon' was actually an Unidentified Flying Object from outer space. In fact, they believe the military actually recovered three or four alien bodies, and recovered the UFO and point to the press release put out by the Military Authorities at the time which stated that they had indeed recovered a UFO. Only for it to then be retracted 24 hours later.
With excellent timing, Lieutenant Walter Haut, who was the PR man at the base in 1947, and who issued both the press releases after the crash, died and left a sworn affidavit to be opened only after his death.
The text was released and 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. 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.
The arguments over whether it was a cover up or just fanciful thinking will continue for some time yet, but 60 years on it still has the power to divide opinion and that's the hallmark of a truly great conspiracy theory.