Who's stealing Christopher Columbus letters from libraries around the world?

In 1492, Christopher Columbus, of course, sailed the ocean blue. And on his journey home, he wrote a letter to his patrons, King Ferdinand and Queen Isabella of Spain, describing his discovery of the new world, and in effect, asking for more money to make another trip. Columbus' voyage marked one of the great plot points in history. Upon his return, his letter was printed and distributed throughout Europe, making for blockbuster news. Columbus' original handwritten letter, penned on the high seas, no longer exists, but some of the printed copies do. Most are housed in prestigious libraries, and for centuries, that's where they've remained. That is, until about 10 years ago, when authorities discovered some of these treasures had been stolen and replaced with forgeries. So began a modern kind of trans-Atlantic quest, as investigators in the U.S. and Europe worked to recover Columbus' missing missives and solve this most unusual international mystery.  

If there is one library in the world you'd think would be impervious to theft, this would be it. The Vatican library in rome houses a vast and unrivaled collection of historic treasures. It is the pope's library, home to manuscripts going back nearly 2000 years. The library is closed to the public, it's a place for scholars only. But Ambrogio Piazzoni, the vice prefect, invited us inside.   

It was here in 2011 that Vatican officials first discovered that one of their prized items, a Columbus letter, had somehow been stolen and replaced with a fake.  

Jon Wertheim: How do you think this happened?

Ambrogio Piazzoni (Translation): Look I do not know. I have no idea how and when it may have happened. Certainly it was an operation carried out as a proper theft. But I do not know when or how.