The arm belonged to a stowaway, who was naturally suffering from dehydration. For some reason, stowaways are often smart enough to get past airport security, but not smart enough to bring water on board.
The plane had arrived from Addis Ababa and made a stopover in Rome, so the man had been locked in the luggage hold for about 20 hours. He has been transported to a federal holding facility, and will be sent back to Ethiopia after being charged.
Officials were quick to point out that the man was not considered to be a terrorist threat.
Despite the large number of international flights arriving in the US every day, stowaway passengers are still fairly rare, and I’m sure the common misconception that the cargo hold is unpressurized helps scare a lot of would-be stowaways out of the idea. Of course, reading that stowaways are immediately sent back to their homeland also makes the whole idea of hiding in the cargo hold rather unappealing.