I really don't think there was a cover-up at all. People reported seeing strange lights/craft, but prototype aircraft for the US airforce were probably being tested out there. I once read an old book by Leslie Watkins, called Alternative Three. Not sure if it was Buzz Aldrin who was interviewed for it, but he supposedly admitted that when the guys landed on the moon, they weren't the first ones there, and that they uttered words of astonishment on seeing some type of vehicle in the distance, but these were bleeped out by ground control during the "live" coverage. Roswell isn't the only place to've been shrouded in mystery though. Alien beings've been reported captured in Mexico, for instance, but since the general public've never been able to survey one, i doubt the stories are true.