Van Meegeren produced a remarkable defense. Nothing of value had left the Netherlands, he claimed: the painting was one of his own creations, produced to fool the snobby experts who had doubted his own artistic ability.
Incredibly, Van Meegeren proved his claim by painting another "lost Vermeer" during his trial. He was promptly acquitted of treason -- and imprisoned for forgery.
[The famed forger Madame Claude Latour was so skilled that some of her depictions of Parisian streets in the style of Maurice Utrillo fooled Utrillo himself, who later confessed that even he was unsure which paintings were his and which were Latour's.]