[Ken H]

There are very few entities in the world who could gather that much loot together, and try to smuggle it across a border. One of my prime suspects would be a drug cartel.

It's a real head scratcher, that's for sure. Here is the original FR thread with a lot of good speculation:

2 Japanese carrying $134 bil worth of U.S. bonds detained in Italy

[livius]

One of the things I read that I thought was very significant is that this was not just a huge bunch of bonds. The quantity was so great that five of them were in a denomination only printed for states.