Complex sentence: The U.S. Government later concluded that the incident likely involved a secret U.S. military Air Force surveillance balloon, while many UFO proponents claim that an alien spacecraft crash-landed with its occupants recovered by the military who subsequently covered up any knowledge of the incident.
Split into simpler sentences: The U.S. Government later concluded that the incident likely involved a secret U.S. military Air Force surveillance balloon. The incident has been the subject of intense speculation by UFO enthusiasts who claim that, contrary to the official explanation, an alien spacecraft crash-landed with its occupants recovered by the military who subsequently covered up any knowledge of the incident.