He was arrested while using a fake ID to evade the police from his first capture and that ID had a fake first name and birthplace, so perhaps that is the reason

He was arrested while using a fake ID to evade the police from his first capture and that ID had a fake first name and birthplace, so perhaps that is the reason. (I never met him -- he died before I was born) Passports were not required back when he left the US, so I doubt he had proof handy and even if he did it was probably a fine line. Showing proof he was American could have made him a target instead of helping.