London and Dubai's international airports have become conduits for billions of dollars of illicit funds, potentially linked to corruption, drug trafficking and other crimes. WSJ's Margot Patrick explains how couriers in one money-laundering operation transported millions in dirty money on flights. Further Reading: - Billions in Dirty Money Flies Under the Radar at World’s Busiest Airports  Further Listening: - How The Government Tied One Couple to Billions in Stolen Bitcoin  Learn more about your ad choices. Visit megaphone.fm/adchoices