Customs officials are investigating what is apparently a case of gold smuggling, one that speaks to the growing level of sophistication among smugglers exploiting budget carriers' tendency to use the same aircraft for both domestic and international flights.

Some media outlets have also pointed the finger at China's wealthy. The argument goes that the rich, having lost confidence in the Chinese yuan and with investment in other assets becoming difficult, are turning to gold smuggling to move their wealth out of the country. They supposedly hire mules to carry the gold from China, as well as places like South Korea and Taiwan, into Japan, where the consumption tax increase has made it easy for them to pay off the carriers and bribe staff at Asian airports.