A little after midnight on March 18th, 1990, as folks were stumblin' out of the bars from a night of celebrating St. Patrick's Day, two men dressed as police officers knocked on the door of Boston's Isabella Stewart Gardner Museum, and were let in by an overnight worker there.  What happened next has been a mystery now for 31 years.

But what authorities and the FBI knew was that more than $500 million worth of artwork had been stolen, 13 pieces of artwork in 81 minutes.

Over the years, the FBI chased various leads across the globe and they now believe that they know who pulled off the heist.  The agency now thinks that the thieves were part of a criminal organization based in New England and the mid-Atlantic states.

They think that the artwork was taken to Connecticut and then the Philadelphia region in the years following the theft, and finally offered for sale in the Philadelphia area years ago. After that, the FBI lost the lead, and they now believe that the two main suspects in the heist are now dead.

FBI.Gov picture - Manet, Chez Tortoni, 1878–1880

Since the heist, empty frames have hung eerily on the walls of the museum, reminding people of the enormous loss that the museum had incurred.

The Isabella Stewart Gardner Museum still offers a $10 million dollar reward for the artwork's return.

The FBI's Richard DesLauriers said authorities believe someone not involved in the theft has seen the artwork without realizing it is stolen. "It's likely over the years that someone, a friend, neighbor or relative, has seen the art hanging on a wall, placed above a mantle or stored in  an attic. We want that person to call us," DesLauriers said.

If you may have a clue as to the whereabouts of the stolen artwork, the man to get in touch with is Anthony Amore, the Director of Security at the Isabella Stewart Gardner Museum.

Look for a brand new 4-part docu-series on NetFlix soon titled, "This is a Heist."

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