It remains the most valuable — and confounding — art heist in history: 13 artworks stolen from Boston’s Isabella Stewart Gardner Museum. Twenty-eight years later, not a single piece in a haul worth half a billion dollars has surfaced. The art, and the thieves who made off with it, remain at large. With first-ever interview, unprecedented access, and more than a year of investigative reporting, "Last Seen" takes us into the biggest unsolved art heist in history. A joint production from WBUR and The Boston Globe.