question about proof Julia boarded the plane
The captain clearly looked at Julia's passport when he was called out by the air marshall to take care of the situation when Kyle said she was missing.
When people go through customs when arriving and leaving a foreign country, their passport is stamped with both a entrance and exit stamp along with the date of each action. Couldn't the captain have simply looked in Julia's passport and noticed that an exit stamp was applied to her passport that very day of the flight?