In a secret meeting in 1981, a low-level Boston thief gave career gangster Ralph Rossetti the tip of a lifetime: the Isabella Stewart Gardner Museum was a big score waiting to happen. Though its collections included priceless artworks by Rembrandt, Vermeer, Degas, and others, its security was cheap, mismanaged, and out of date. And now, it seemed, the whole Boston criminal underworld knew it.

Nearly a decade passed before the Museum museum was finally hit. But when it finally happened, the theft quickly became one of...