The script is based on a Wired magazine article titled "The Untold Story of the World's Biggest Diamond Heist," by Joshua Davis.
The article (Paramount acquired the rights in March 2009) described the true story of a diamond heist in Antwerp, Belgium. It was in early 2003 that a small group of Italian thieves circumvented 10 layers of security to access a vault beneath the Antwerp Diamond Center. They stole $100 million in diamonds, gold and jewelry (the actual value is still not known).
Over a six-year span, Davis was able to get multiple interviews with the person who organized the whole thing; he is presently incarcerated in a Belgian prison. He divulged how they pulled it all off.