They have probably been doing this for awhile with smaller amounts. Paid off all the appropriate people within the Italian government (government payoffs are normal business practice in many parts of the world). This time however someone learned how much was being moved and they got caught.
Initial reports I saw referred to these guys possessing so-called Kennedy bonds, 10 I think, each with a $1 billion face value. That item is missing in later reports of this story. Interesting.