BUENOS AIRES, Argentina -- Until a fateful morning last August, María del Luján Telpuk was an anonymous 27-year-old airport policewoman here. Then fate swooped down in the form of a Cessna Citation jet arriving from Caracas, Venezuela.

Inspecting the passengers' luggage as it passed through the X-ray machine, Ms. Telpuk noted that one suitcase contained the shapes of "six perfect and very dense rectangles." They turned out to be about $800,000 in cash carried by Guido Antonini Wilson, a mysterious businessman...