Isleworth Mona Lisa
According to Leonardo's early biographer Giorgio Vasari, Leonardo had started to paint "Mona Lisa" in 1503, but "left it unfinished". However, a fully finished painting of a "certain Florentine lady" surfaced again in 1517, shortly before Leonardo's death and in his private possession. The latter painting almost certainly is the one that now hangs in the Louvre. Based on this contradiction, supporters of the authenticity of the "Isleworth Mona Lisa" claim it is the unfinished "Mona Lisa", made at least partially by Leonardo, and the Louvre "Mona Lisa" a later version of it, made by Leonardo for his own use.
Mona Lisa
French poet Guillaume Apollinaire came under suspicion and was arrested and imprisoned. Apollinaire implicated his friend Pablo Picasso, who was brought in for questioning. Both were later exonerated. Two years later the thief revealed himself. Louvre employee Vincenzo Peruggia had stolen the "Mona Lisa" by entering the building during regular hours, hiding in a broom closet, and walking out with it hidden under his coat after the museum had closed. Peruggia was an Italian patriot who believed Leonardo's painting should have been returned for display in an Italian museum.