Whilst our man is waiting to have his papers checked, we see a fax arriving in the guard house. The fax machine is clearly a small thermal unit typical of the era - but we hear the sound of a dot-matrix printer.
As he sneaks into his apartment to get the drop on his friend, we see two crew faces reflected in the glass of one of the pictures on the hallway wall.
Logically, it would not have been necessary for Higbe to be physically present to reveal to the American authorities the damning knowledge he possessed since he had already revealed it to Crawford who could have done it for him.