An enigmatic disappearance

Another Mona Lisa Mandela Effect?

First we had her smile changing over time, then the non-mystery over her identity. Now it turns out many people today are surprised to learn the painting was stolen in 1911. 

The theft was actually an inside job. In 1911, Vincenzo Perugia had worked at the Louvre for a time and was familiar with the daily routines and procedures of the staff. One day, he and two accomplices wore the same white smock as them and hid when the gallery closed for the evening. He then removed the painting from its frame, and in the morning when it opened up just walked right out of the door with it under his smock. They boarded the 7:47am express train with it, mingling with the morning city commuters, and got clean away with what just became the most famous painting in the world.

He wasn't doing it for the money. He believed the painting was the property of Italy and was attempting to return it to what he saw as it's rightful home. For this reason he served a very light prison sentence, which no doubt made him smile, enigmatically, when he heard that news.

Fame

It's difficult to comprehend today, but outside the art world the Mona Lisa wasn't well known.

The 'Mona Lisa' wasn't even the most famous painting in its gallery, let alone in the Louvre."

-- James Zug, Historian

Theft

Astonishingly, it was 28 hours before anyone even noticed the painting had been stolen. Vincenzo Perugia had removed the safety glass which he'd been hired to install in the first place.

Speculation regarding who stole it was rife. This was 1911, and relations were becoming strained between Germany and France ahead of WW1, so there were people who thought the Kaiser had done it. Some had noticed rich foreigners buying up the art of France - even JP Morgan was personally suspected.

It was recovered after a bungled attempt to sell it, but what really overshadowed this 2.5 years after the theft, was the outbreak of World War 1. This is most likely why so few people are even aware of the whole episode - people had much bigger things on their minds then.