Twenty years ago this week, 13 major artworks by Vermeer, Rembrandt, Degas, Manet, and others were swiped from Boston's Isabella Stewart Gardner Museum. The world's biggest art heist still baffles investigators who have no viable leads.

A $5 million reward is offered for the recovery of all, or any, of the $500 million worth of stolen art. The paintings are not salable, too well-known to be sold on the underground.

Even Myles Connor, the convicted art thief who has long boasted of knowing who did it, has come up empty-handed. Connor, and others, have been given immunity if they help find the paintings. The actual thieves would not be given any reward.