It is more likely that a military test plane crashed at Rosewell. The government has to develop and test new planes, and these would be kept secret for military purposes. It would make far more sense if it were a plane that people weren't familiar with rather than a UFO.
There is no possible way that the government has been able to keep the discovery of a UFO under wraps for over 50 years. There are many conspiracy theorists that say it is possible that the US government is hiding this discovery but the facts are more clearly evident that this is not true.