The men intent on their rocket preparation don't see a dark shape slip back into the woods. The freedom of America may depend on their work, you can't blame them for being intent on doing a good job.
Another soldier comes over to help investigate. The guard is gone, but there is a small amount of blood on the ground where he was standing. No one heard a thing.
The radioman calls for more soldiers to both help in the search and to secure the scene. The Quick Reaction Force is put on alert to respond.