The amount of client funds missing from MF Global’s books has doubled to $1.2 billion—nearly a quarter of the investment firm’s $5.45 billion in customer money. Previous estimates had put the shortfall at $600 million. The number grew, however, as regulators scoured MF Global’s sloppy books. People familiar with the government’s investigation tell Financial Times that MF Global and its former chief, former New Jersey governor Jon Corzine, appear to have used customer funds to meet margin calls as they prepared the company for a sale. Firms are required under U.S. law to keep client funds separate from the company’s own house funds.