And the plot thickens.

While the debate over exactly who is responsible for Bear Stearns' swift demise continues, it's becoming clear that certain traders made a killing during that fateful week in March.

On March 11, the day the Federal Reserve announced plans to extend its lending facilities to investment banks later in the month, someone bet $1.7 million that shares of Bear Stearns would lose half their value in just a week. According to trading data examined by Bloomberg, a single trader or a group of traders took out 5.7 million put options with a strike price of $30 expiring in one week. At the time, Bear was trading for $62.97. Another, smaller trade bet that the stock would fall to $25 per share in the same time frame.

Options specialists call the trade preposterous. "It's not even on the page of rational behavior, unless you know something,'' Thomas Haugh, general partner of the options trading firm PTI Securities & Futures, told Bloomberg.

Ah yes, there's the rub. Did this trader know something that the rest of the world did not? Or did these traders place the bet as part of a master plan to drive Bear Stearns into the ground?  

As the story of Bear Stearns' unraveling unfolded in the days following the mysteriously bearish trades were made, more options traded with strike prices as low as $5, even when the stock was still in the $50s. Such a trade is called a "bankruptcy put," meaning the trader is betting the company will go bankrupt.

It's hard to imagine just what kind of insider information these traders might have had at the time. Did they know there would be a run on the bank that would force it into a fire sale? Or did their bearish bets help to cause it? Finding the precise line between cause and effect may not be easy for regulators.

The Securities and Exchange Commission, which declined to comment on the Bloomberg story, is investigating the trades placed during the days before it agreed to be sold to J.P. Morgan for just $2 a share. Outraged shareholders eventually pushed J.P. Morgan to offer $10 per share a week later.

Other financial stocks, such as Lehman Brothers, Fannie Mae, and Freddie Mac, have experienced significant nosedives since the Bear debacle, which prompted the S.E.C. to put limits on short-selling practices for certain stocks. Those temporary rules expire on Wednesday, and it's not clear to what extent they helped to stabilize the market.