> Third, how FBI ever knew of him buying a ticket? US is not East Germany where all ticket sales are wired to STASI in real time.

The TSA has exactly this system in place.

> This is supported by the fact that he was detained "minutes before boarding." Probably, it was only the fact of him passing the border control that was visible to FBI, the moment they saw it, they came with a rushed arrest warrant.

Or they were waiting for incontrovertible evidence of attempted flight from the country.