The theft last week of an important Leonardo painting “highlights the difficulties of safeguarding valuable works of art while allowing access for the public. It is the latest in a series of robberies of art works so famous that they would be impossible to sell on the open market. Still missing are Rembrandt’s “Storm on the Sea of Galilee”, and Vermeer’s “The Concert”, stolen in March 1990 from Isabella Stewart Gardner Museum in Boston by thieves dressed as policemen. Even art world insiders can only speculate as to their whereabouts and the motives of such robberies. Theories being put forward by the police and experts for this latest theft include links to terrorist groups and drugs gangs. Benvenuto Cellini’s salt, a masterpiece of 16th-century goldwork, was stolen in May from Vienna’s Kunsthistorisches Museum.”