This past May will go down as a fateful month in the history of European museums. An unknown culprit broke into the Musée d’Art Moderne in Paris one night and, cool as a cucumber, cut five masterpieces by Braque, Léger, Matisse, Modigliani and Picasso out of their frames. The canvasses are worth about a hundred million euros all told. Afterwards people puzzled over why anyone would steal such famous works that can’t be sold legally anywhere. The answer is “artnapping”: art thieves squeeze a museum, or rather its insurers, who would rather hand a lavish sum to a middle-man who guarantees the return of the works than award a much higher indemnity to the owners. Only – and here’s the rub – there’s no insurer for the pictures in Paris, which hung in the museum uncovered – and actually unprotected: the alarm system had apparently been out of order since March.

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