'Younger Mona Lisa' mystery

A painting attributed to Leonardo da Vinci representing Mona Lisa, is displayed during a presentation in Geneva, Switzerland, Thursday, Sept.27, 2012. The Mona Lisa Foundation, a non-profit organization based in Zurich, presents a painting and historical, comparative and scientific evidence, which demonstrates that there have always been two portraits of the Mona Lisa by Leonardo da Vinci, the 'Earlier Version,' made ten years earlier than the 'Joconde' that is displayed in Le Louvre in Paris, France. (AP Photo/Keystone, Yannick Bailly)
A painting attributed to Leonardo da Vinci representing Mona Lisa, is displayed during a presentation in Geneva, Switzerland, Thursday, Sept.27, 2012. The Mona Lisa Foundation, a non-profit organization based in Zurich, presents a painting and historical, comparative and scientific evidence, which demonstrates that there have always been two portraits of the Mona Lisa by Leonardo da Vinci, the 'Earlier Version,' made ten years earlier than the 'Joconde' that is displayed in Le Louvre in Paris, France. (AP Photo/Keystone, Yannick Bailly)

A package of diaries said to have been posted to the United States from Britain in the 1960s could provide a vital clue to the origin of a controversial portrait presented in Geneva last month as Leonardo da Vinci's original "Mona Lisa."