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The Haskell Free Library, which straddles the U.S.-Canada border, is home to an array of novels, an opera house and — for a brief time — international gun smugglers.

The heritage building was built in 1904 and is the only library in the world to straddle a border, between the towns of Derby Line, Vt., and Stanstead, Que. There is a black line on the library floor marking the divide.

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You enter the building through the U.S., but the circulation desk and most of the books are in Canada. The reading room is in both countries. The building’s unique layout may be why it was an attractive location for a Montreal man to smuggle handguns into Canada.

Stashed guns in library washroom

On Monday, 40-year-old Alexis Vlachos pleaded guilty to smuggling 100 handguns from the U.S. into Canada and using the library as a drop-off point.

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Vermont prosecutors said between July 2010 and April 2011, Vlachos worked with two Americans who purchased dozens of handguns in Florida and then drove them to Vermont to smuggle them into Canada.

Black tape marks the U.S.-Canada border inside the Haskell Free Library and Opera House.

On March 25, 2011, the two Americans stashed a bag of around 20 firearms in the washroom of the Haskell Library and left. Vlachos then walked into the building and retrieved the bag, according to court documents. He then sold the guns in Quebec, prosecutors said.

But the drop off caught the eye of an attentive librarian and police started watching the smugglers from then on, according to court documents.

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A couple of weeks later, one of the Americans bought 34 guns from a dealer in Florida and then drove them to a remote section of northeastern Vermont, near Lake Wallace. Vlachos then hiked into the forest and met the accomplice, handing over $18,000 in cash in exchange for the firearms.

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Vlachos was then arrested by Canadian police and now faces up to 20 years in prison. His sentencing is set to take place in May.

One of the American accomplices, Annette Wexler, previously pleaded guilty to conspiring to make false statements to licensed gun dealers and unlawful exportation, according to court documents.

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How the building is divided

The divided library is not an accident. According to the library’s website, the Haskell family purposefully built it along the border to promote cross-border interaction and friendship.

There is a line of tape dividing the American and Canadian sides of the building.

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Rebel Sargent, 6-months-old, of Holland, Vt. looks at her book on the Quebec side of the border line going through the Haskell Free library. Stan Grossfeld/The Boston Globe via Getty Images The oprea house is seen at the Haskell Free Library and Opera House. AP Photo/Toby Talbot The Haskell Free Library and Opera House straddles the U.S.-Canada border. DON EMMERT/AFP/Getty Images A sign next to the Haskell Library and Opera House, Wednesday, May 23, 2007, in Derby Line, Vt., reads in English and French urging visitors to report to customs and immigration immediately. AP Photo/Alden Pellett

The opera house is also split in two. The audience sits in the U.S. to watch a show while the stage is Canadian territory.

The entrance of the library is watched 24 hours a day by the U.S. Department of Homeland Security.