Police arrested two suspects in Berlin on Wednesday for theft of a 100 kilogram (220 pound) coin from Bode Museum in March this year. The coin, however, is yet to be found.

The stolen coin, called the "Canadian Big Maple Leaf" has a face value of $1 million, and is made of  pure 24-carat gold, which means it is worth is more than its face value — about $4.2 million.

According to Smithsonian.com, the Royal Canadian Mint produced only five copies of the coin, one of which was displayed behind bulletproof glass at Berlin’s Bode Museum. Authorities were perplexed how it was stolen as the weight of the coin is as much as a refrigerator’s. The Big Maple Leaf was on display in the museum since December 2010, on a floor below the window in its own bulletproof case. It was surrounded by other, smaller gold coins. According to the New York Times, the bulletproof glass “appeared to have been violently shattered." The other smaller coins were, however, left untouched.

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The coin is about 21 inches in diameter and over an inch thick. The website of Royal Canadian Mint says the coins were originally conceived as a unique showpiece to promote the mint's new line of 99999 pure 1 oz Gold Maple Leaf bullion coins. After several interested buyers came forward, the Mint decided to make a very limited number of coins available for sale. To date, five of these gold bullion coins, have been purchased by investors from Canada and abroad. The coin in question was loaned to the Bode Museum from a private collection in December 2010.

While one side of these coins features a hand-polished maple leaf design by Royal Canadian Mint artist and engraver Stan Witten, the other bears the effigy of Queen Elizabeth II by celebrated Canadian portrait artist Susanna Blunt. The first Big Maple Leaf coin was produced in 2007. Guinness World Records deemed it the world’s largest going coin later that year. The coins are manufactured at the Mint's Ottawa facility.

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In July, police published still photos made from surveillance video asking the public for help in finding the thieves who had stolen the coin from the museum.

According to the police, at least two burglars broke into the museum at night, using a ladder to climb to a window from elevated railway tracks. They grabbed the coin, loaded it onto a wheelbarrow and then carted it out of the building and along the tracks across the Spree river before descending into a park on a rope and fleeing in a getaway car. "We assume that the two suspects match the ones seen on the video footage from surveillance cameras," police spokesman Winfrid Wenzel had said at the time of the burglary, according to CBS.

The Bode Museum has one of the world's largest coin collections with more than 540,000 items.