The mighty greenback is a much more frequent flier than you might think.
The popularity of the US dollar as a street currency outside the US means that substantial quantities of US banknotes are shipped outside the US every year. The export of US dollars is by no means accidental: it is in every government's interest to promote the usage of its banknotes because of the economic phenomenon known as seigniorage whereby a state profits from the issuance of its banknotes. The US Federal Reserve profits from the use of the US dollar abroad and helps orchestrate its physical movements.
Thus the US exports vast quantities of banknotes, especially to soft currency areas of the world (e.g. Russia) or those areas where the the local economy has effectively dollarised (e.g. much of Latin America). Three-quarters of all 100 dollar notes are held outside the US, according to the Federal Reserve Board.
I recall reading a fascinating article in New York Magazine on the movement of banknotes several years ago, featuring the weekly US banknote haul from JFK to Moscow in the belly of a Delta 767, but I can't so far find the piece on the web.
As to the fact that in this case the currency was headed back to the States: notes wear out and require replacing. The clever thieves in this haul will have received the perfect stash of out of sequence, used notes. It sounds like a terrific piece of criminal work!
Minor edits for content.
[ 11 February 2002: Message edited by: J-Class ]</p>