4. Fake Policemen Rob The Gardener Museum on St. Patrick's Day

Stolen: Rembrandt, Lady and Gentleman in Black and The Storm on the Sea of Galilee 
Johannes Vermeer, The Concert
Edouard Manet, Chez Tortoni
Location: Boston, Massachusetts
Year: March 1990
Worth: $300 million

On St. Patrick's Day in Boston, two men in police uniforms (even donning fake mustaches), told security guards they were investigating a disturbance at the Isabella Gardener Museum. They handcuffed the guards and stole more than a dozen pieces by cutting them from their frames in 90 minutes. Convicted art thieves, dealers, South American drug cartels, the Irish Republican Army, Japanese underworld figures, and Boston-area mobsters were all suspected to be culprits of what's considered the biggest unsolved heist in US history. No one has been charged with the thefts and the pieces are still MIA.