Things get tougher for former Governor Jon Corzine today, as he makes his third appearance before congress.

He faces the toughest committee yet, amid new allegations that he may well have known about an alleged illegal loan and misuse of investor money.

More than a billion dollars of investor funds remain missing, and Corzine continues to claim he does not know what happened to it. Corzine was CEO of MF Global as it plunged into the eighth biggest bankruptcy in American history.

Lawmakers, regulators and law enforcement officials are trying to find out what happened to the money.

Corzine is set to appear this afternoon before the House Financial Services Oversight and Investigations Subcommittee, a Republican-led panel known for aggressive questioning.

It's his first public appearance since a financial-exchange executive alleged Tuesday that Corzine knew more than he's admitted about the firm's transfer of client money in its final days.