Three former Fannie Mae executives, including the company’s one-time CEO, have petitioned a federal judge to toss the securities fraud case the government filed against them late last year. Filed last week in the U.S. District Court for the Southern District of New York, the motion to dismiss contends the Securities and Exchange Commission is thin on proof that the GSE, at the direction of the then top executives, failed to disclose to investors the companies’ exposure to subprime mortgages prior to the 2008 housing market crash.