The New York Times DealBook blog just put out a fine piece on the collapse of MF Global: A Romance with Risk That Brought on a Panic by Azam Ahmed, Ben Protess, and Susanne Craig (December 11, 2012). It’s the most comprehensive summary of the events that led to the firm’s bankruptcy that we’ve seen so far. Until the investigations are done and the books are written, it’s a good source for thinking about the credit risk lessons to be learned in MF Global’s sad story.

MF Global seems to have made a lot of risk management mistakes. It took on a big dose of market risk with its $6.3 billion exposure to the European debt crisis – over the objections of its senior risk manager. With only $1.4 billion in capital, the company could barely afford to take any losses.

There may have been operational risk issues at the firm as well. About $1.2 billion of client money has gone missing, and after weeks of searching the company’s records it’s still not clear where most of it is. At best, this is a serious systems failure; at worst, it could be a lot more sinister.

But the fatal risk at MF global was a form of credit risk called counterparty risk. That’s the risk that a firm involved in a trade fails to pay what it owes. Counterparty risk is where market risk and credit risk intersect: as a company’s trading losses grow, its ability to pay decreases.

Moody’s downgraded MF global from Baa2 to Baa3 in October, citing exposure to European sovereign debt, a regulatory capital shortfall, and poor risk management. The market had been concerned about MF global for months, but the downgrade made it official. MF global was a poor counterparty.

That triggered collateral calls, with trading partners and clearing houses demanding that the firm either close out its positions or post more collateral – usually in the form of cash. The firm that cleared MF Global’s sovereign debt trades demanded $300 million in cash collateral alone. MF Global’s risk challenges suddenly became a fatal liquidity problem.

That should not have been surprising. The same thing happened to Lehman Brothers and even to Goldman Sachs. The combination of collateral demands and a runoff in repurchase financing drove Goldman’s liquidity pool from $120 billion to $57 billion in just four days after Lehman went under.

MF Global’s counterparty credit squeeze suggests the likely explanation for the missing client money: desperate to meet collateral calls, the company used client funds to try to plug the holes in its liquidity dike. That changes the nature of MF Global’s operational risk problem. It’s worse than a mistake; it’s a crime.