What would make a man sign a sworn affidavit (to be released only after his death) to the effect that he saw spacecraft debris and alien bodies at Roswell? If it's a hoax, it's a peculiar one. Hoaxes are generally revealed after the instigator dies. To have one commence with the hoaxer's death would certainly be a novel twist.

One possible explanation is that, 60 years ago he did see something that made quite an impression, and what that was and what it meant grew in his mind over the years. Another is that the government was playing a very subtle game at Roswell: using debris from an experimental balloon project as a pretext for leaking a false story that the US had recovered a UFO -- a head-fake at the Soviets. Let them worry about what we're going to do what that alien technology.

If the latter is true, Jesse Marcel was a just a pawn in that little game. The authorities at Roswell may have circulated rumors of alien bodies -- maybe they even had a couple of fake alien bodies floating around the place for a couple of days -- exactly so stories like Marcel's would get out and find their way back to the Russians.

Jerry Pournelle explores both of these possibilities, and gives one of the better last words on Roswell that I've ever read:

But most importantly I think that if the US had any hidden technology in 1964 I would have known about it. Why would they hide it from Systems Command? We were structuring the 1975 force. What would anyone in government hide it for? We were scared stiff of the USSR missile threat, hard pressed to find any war fighting strategy that made sense and would allow for the survival of the American people; we needed everything we had. We had the highest clearances because we were doing a survey of ALL RELEVANT TECHNOLOGIES so that we could evaluate force structure designs. We had an absolute need to know, and a directive to all parts of USAF to cooperate. Ye gods, why would the government hide alien technology from us? Where are these secret materials NOW?

Those a pretty good questions. And even if the government had decided that Systems Command shouldn't know about it, somebody would have known about it. Unless you're ready to buy into an Area 51 scenario like the one described in Independence Day where even the president doesn't know what we have, the story just doesn't stand up.

Nonetheless, it is a great story...

UPDATE (semi-related): Looks like the aliens are now treating us to 3-D images in their crop circles. I wasn't sure before, but now this cinches it: those aliens are definitely using computers!