A: "Knock, knock." "Who's there?" "Police. We got a call there might be some burglars in this museum trying to steal some art?" "No, not here." "Okay, well, we're going to have to take some paintings with us and dust them for prints." "Sure. Come on in." Fake cops, they'll get you every time.

On March 18, 1990, in what still ranks as the biggest art theft in U.S. history, two thieves dressed as cops made off with masterpieces worth over $300 million (again, over $300 million!) from Boston's Isabella Stewart Gardner Museum. The two men, dressed as Boston policemen, pretended to respond to a disturbance. They cuffed the security guards, then helped themselves to 13 paintings, including works by Vermeer, Manet, and Rembrandt.

While none of the paintings has yet been recovered, a popular theory has developed that the heist may have been masterminded by — get this — the Irish Republican Army. (Who knew they were art lovers?). It's theorized that the IRA, working in conjunction with Irish gangsters in Boston, planned to ransom the paintings (now alleged to be hidden in Ireland), then use the money for gun-running. Of course, IRA spokesmen vehemently deny any kind of involvement (i.e. in regard to those paintings, they say they were framed).