Mystery of a masterpiece

Summary/Review: In October 2009, a striking portrait of a young woman in Renaissance dress made world news headlines. Though it had been purchased two years earlier for around $20,000, the portrait is now thought to be an undiscovered masterwork by Leonardo da Vinci worth more than $100 million. Did cutting edge imaging analysis help tie the portrait to Leonardo? Nova meets a new breed of experts who are approaching 'cold case' art mysteries as if they were crime scenes.