Wired has a great story on The Untold Story of the World's Biggest Diamond Heist.
Read the whole thing and you'll get some good tips should you want to plan your own heist but you won't be able to figure out who got the diamonds.
They were accused of breaking into the Antwerp Diamond Center’s supersecure vault and stealing $100 million in diamonds, gold and jewelry. The loot was never found, but their trash was.