Laurie Hurwitz has a story in the current ARTnews on a forthcoming documentary about "the infamous theft of August 21, 1911, when an Italian mason named Vincenzo Peruggia walked out of the Louvre with the Mona Lisa."
Here is Peruggia's Wikipedia enty. Here is a fairly recent piece from Time magazine, which put the theft on their list of the Top 25 crimes of the twentieth century.