Specifically with regards to this nugget you mentioned (from the article):
Many of Cordier's clients had qualified Individual Retirement Accounts at FCStone. Generally, money in such accounts is not supposed to be used for the risky type of trading that Cordier did on the clients' behalf.
How does it work if your IRA goes negative by more than the annual contribution? Can you add money to bring it back up to zero in any amount?
What happens if you can’t cover your losses? Aren’t IRAs somewhat protected from some judgements? What happens next for the investors, and who ends up taking the remaining losses?