Federal regulators on Thursday filed civil charges against former MF Global Holdings Ltd. Chief Executive Jon S. Corzine and a top lieutenant for overseeing the misuse of almost $1 billion in customer funds, saying Mr. Corzine "bears responsibility" for the New York commodities brokerage's 2011 demise. The Commodity Futures Trading Commission's complaint cited conversations not previously disclosed purportedly showing Mr. Corzine played a more active role in the firm's activities than he had suggested in the past. The lawsuit, filed in U.S. District Court in Manhattan, comes as a new blow for Mr. Corzine, whose reputation—built on a career as...