He knew that the museum would be closed Monday morning for repairs, and after hiding inside the museum the whole night, Vincenzo donned a smock and swept the Mona Lisa off her feet with one furl of his fabric. Seeing at least 10 people working nearby and being illegally in the possession of the most famous piece of art known to the planet might weaken the resolve of lesser men, but Vincenzo kept his cool.
He moved down a nearby stairway, probably humming the Mission: Impossible theme to himself, and freed Mona from her frame. When the downstairs exit was locked, Vincenzo thinking either on his feet or like a caveman ripped the doorknob off the door and convinced a nearby plumber that it was stolen. A reminder: The dude with the Mona Lisa on his person was making a fuss to a plumber about a stolen doorknob. The plumber let him out and bam: The crime was complete.
Apparently basic skepticism hadn't been invented yet.
Vincenzo expected a hero's welcome back in Italy and a hefty reward for the painting, but Florence's Uffizi Gallery just fluffed his balls long enough to authenticate the painting and put the poor dumb sap under arrest. Vincenzo was sentenced to jail, but served minimal time as the patriotism of his act was considered a "mitigating factor." Remember that the next time you appear in traffic court. You weren't speeding. You were speeding for America.
Those pedestrians you hit were probably terrorists or something.