We know absolutely nothing about the Roswell crash for certain, except that it had absolutely nothing to do with extra-terrestrials. Everything is in doubt. Excpet that these events occurred in 1947.
First the crash occurred on three weeks before July 8, then July 4, then July 2. You see the witnesses who first came upon the debris can't seem to get straight dates. The Air Force has been less than precise, and far less than helpful, but the general consensus is that the crash occurred on July 2, 1947 and that the clean up took place around July 14.
Second, there was one crash sight, then five, then finally eleven. There's always going to be some entrepreneurial crackpot who can find another crash site and provide some burned pieces of metal.
Third, the Air Force has claimed that the debris was a flying disk, a downed weather balloon, a secret project called Mogul, a secret project called Project High Dive, and several other cases of really dumb disinformation.
Fourth, no alien bodies were recovered, then two alien bodies were recovered, the four aliens bodies were recovered, then one of the aliens was still alive, then the aliens are being stored in Area 51, then there's an alien autopsy film, but it's a fraud, there are four witnesses, the eight, then only three. One witness says that her fire-fighter father was part of the recovery team, but she also states that the recovery was a super-duper-secret military operation with no civilians. Of course these witness accounts are only reported 31 years after the events.
Fifth, some key witnesses report being intimidated by the military to change their stories. One witness is supposed to have been in military custody. Turns out he was in journalist custody and appears at the press conference with a journalist who was staying at his house. The strange men in black (who have no sense of humor that we're aware of), are seemingly very powerful and yet have no power at all to prevent the countless ufo book authors from publishing their lurid theories.
Sixth, the best witness, Colonel Thomas Dubose, is supposed to have claimed that there was a cover up of information about the crash, that the debris he found in Roswell had been switched without his knowledge. But in interviews with ufologists, Dubose denies any switching categorically.
Seventh, ufologists love Roswell, then they fight to have the secret information about it declassified. Lazar and the rest of the loonies embellish the nonsense, make up silly stories which they change any time they actually say anything that can be corroborated and later proven false. They cry out that the conspiracy is out to discredit them when the truth is, even the ufologists now believe that Roswell was the nothing it had always been.
On the other hand, anthropologists have studied the Roswell incident and subsequent brouhaha and concluded that it takes the form of myth and myth making. While we on earth worry about our jobs, our families and our homes, we also glory and revel in our own cultural mythologies consisting of Elvis and Bruce Lee surviving spectacular deaths, like Osiris or Odin, extra-terrestrials capturing and impregnating our women (like Ganymede or Persephone). The black helicopters and men in black are like djinn or leprechauns or harpies. We have seemingly constructed our own wonderful mythologies.