$6 Trillion In US Bonds Seized In Zurich, Said To Pose "Severe Threats To International Financial Stability"

Back in the summer of 2009, a peculiar story circulated when two Japanese individuals were arrested trying to smuggle $134 billion in US bonds into Switzerland from Italy. The story quickly died down after it was subsequently reported that the bonds were merely fake bearer bonds. Nobody heard much about it since then. Until today, when out of the blue we get a new story which blows that one out of the water. According to Bloomberg, "Italian anti-mafia prosecutors said they seized a record $6 trillion of allegedly fake U.S. Treasury bonds, an amount that’s almost half of the U.S.’s public debt." From here the story just gets weirder: "The bonds were found hidden in makeshift compartments of three safety deposit boxes in Zurich, the prosecutors from the southern city of Potenza said in an e-mailed statement. The Italian authorities arrested eight people in connection with the probe, dubbed “Operation Vulcanica,” the prosecutors said. The U.S. embassy in Rome has examined the securities dated 1934, which had a nominal value of $1 billion apiece, they said in the statement. Officials for the embassy didn’t have an immediate comment." ...And weirder: "The individuals involved were planning to buy plutonium from Nigerian sources, according to phone conversations monitored by the police." ...And really, really weird: "The fraud posed “severe threats” to international financial stability, the prosecutors said in the statement." Ok great, however one thing we don't get is just how can $6 trillion in glaringly fake bombs be a "threat to international financial stability."
More from Bloomberg:

The financial fraud uncovered by the Italian prosecutors in Potenza includes two checks issued through HSBC Holdings Plc in London for 205,000 pounds ($325,000), checks that weren’t backed by available funds, the prosecutors said. As part of the probe, fake bonds for $2 billion were also seized in Rome.

HSBC spokesman Patrick Humphris in London declined to comment when contacted by telephone.

Phony U.S. securities have been seized in Italy before and there were at least three cases in 2009. Italian police seized phony U.S. Treasury bonds with a face value of $116 billion in August of 2009 and $134 billion of similar securities in June of that year.

The U.S. Secret Service averages about 100 cases a year related to bonds and other fictitious instruments.

As a reminder, total US debt in circulation is just over $10 trillion. So if the allegedly "fake" bonds were sufficiently threatening to put international financial stability at risk, just what is going on here?
Some more from the BBC:

US officials confirmed that the bonds were counterfeit.

Fake US securities have been seized in Italy before and there were at least three cases in 2009.

But this case is on a different scale to previous investigations as the fake bonds have a value equivalent to almost half of the entire US debt pile.

"Everything began with an investigation into mafia clans in the Vulture-Melfese area in the southern Basilicata region," said Giovanni Colangelo, the head of the prosecutor's office in Potenza.

Here is what the bonds look like:

And here is where they were kept: