In 1986 and ’87 I worked as a security guard at the Isabella Stewart Gardner Museum. For most of that time I was a night guard. We weren’t allowed to draw while on duty, but I always carried a small sketchbook, and when I was alone I’d draw studies of the artworks that impressed me. Among those were Vermeer’s “The Concert’’ and Rembrandt’s “The Storm on the Sea of Galilee’’ - two of the masterpieces stolen in 1990, in what remains the biggest unsolved art heist in history, with a total value of $500 million.