Peruggia at the trial in Florence. Wikimedia Only when the painting's empty frame was found on a service stairwell, did Louvre officials began to suspect the worst.
Some 60 detectives swept through the museum. Despite the fact that Peruggia left generous fingerprints on the glass that covered the painting, the lead was not followed up.
The theft was a sensational event, and thousands flocked to see the empty space between Titian's "Allegory of Alfonso d'Avalos" and Correggio's "Mystical Marriage" in the Salon Carré.
It was assumed that some genial mastermind lay behind the theft: even Pablo Picasso and his friend, the poet and art critic Guillaume Apollinaire were questioned as suspects in the theft (they both had previously purchased several Iberian statuettes stolen from the Louvre's archaeological collections.)
"The 'Mona Lisa' was only two miles from the Louvre in the tiny room of Vincenzo Peruggia. He lived there with the masterpiece for nearly 2 and half years," Medeiros said.
Then in December 1913, Peruggia brought the painting to an art dealer in Florence, claiming to be an Italian patriot.
He had hoped to be rewarded by the Italian government for his efforts. But instead of being compensated, he was jailed.
However, the court gave him a lenient sentence: overrall, he served a little over 7 months.
Peruggia's letters to his parents as well as a 61-page report done by a court-appointed psychiatrist, provided Medeiros with the final clues of the man's true motive for stealing the 'Mona Lisa'.
"It wasn't what his daughter Celestina would want to hear," Medeiros said.
According to the filmmaker, Peruggia committed the theft alone and for his own reason - and it wasn't patriotism.
"He was hoping to make his fortune. He speaks nothing of wanting to help his country, but writes he will be doing something to bring a better life to all of his family," said Medeiros.
The documents reveal that Peruggia was tired of his painting job because it was making him physically ill (he had lead poisoning.)
He no longer wanted to travel to Paris to find work because as an immigrant he was poorly treated by his co-workers. And he was a lonely man tired of being away from his family.
"To him, stealing the Mona Lisa and returning it to Italy was his ticket out of this life into a better one. It didn't turn out that way," Medeiros said.
While seeking worldwide distribution, "The Missing Piece" will be shown at two test screenings in Philadelphia on August 21st and August 22nd.