Federal regulators say  hundreds of millions of dollars of customer money  is missing from MF Global, the brokerage firm which filed for bankruptcy on Monday. It is unclear where the estimated $700 million has gone, and no one has yet been accused of wrongdoing. Headed by former New Jersey governor Jon Corzine, MF Global made  risky bets on the European debt crisis. The Dow dropped 276 points in reaction to the news of the implosion,  reminiscent  of the Lehman Brothers collapse in 2008. Joe Nocera, op-ed columnist for The New York Times, explains how Corzine drove MF Global to bankruptcy, and compares the collapse to what happened at Lehman.  Rachel Donadio, Rome bureau chief for The New York Times, reports on the latest from the European debt crisis – news that Greece will hold a referendum on its new aid package, possibly putting austerity measures to a popular vote.