In retrospect, the most intriguing sub-plot in the collapse of the sub-prime mortgage market has been not the size of the losses but their distribution.

Wall Street firms have a talent for getting themselves into trouble together. They all were long Internet stocks when Internet stocks collapsed and they will all be long North Korean credit-default swaps whenever North Korea gets hot and then crashes.

What's odd about the subprime crash is Goldman Sachs Group Inc. A single firm took a position contrary to the rest of Wall Street. Giant Wall Street firms are designed for many things, but not, typically, to express highly idiosyncratic views in the market.

Even more surprising is how little Wall Street seems to have dwelled on how and why Goldman Sachs made its killing. There are insane conspiracy theories - for instance, that former Goldman chief executive officer and current US Treasury Secretary Henry Paulson tipped his old pals, etc. (But then, how did HE know?)

There is also the widely held opinion that people who work at Goldman Sachs are just smarter than ordinary people - hence the lust to hire former Goldman employees to run other Wall Street firms, as Merrill Lynch & Co. did. (But why would any trader who could systematically beat the market waste his time at Goldman Sachs?)

So far as I can tell, there has been only one attempt to explain this strange event, and that was by a journalist, Kate Kelly of the Wall Street Journal.

Ms. Kelly's very good piece offered up the sort of irrelevant details - this little piggy ate which sandwich for lunch as the market crashed, which trader went to the gym at which odd hour to relieve the incredible stress of gambling with billions of dollars of other people's money - that leaves the reader, along with employees of Goldman Sachs, feeling as if someone inside Goldman must have spilled the beans.

But Goldman did not co-operate with the Journal, was actually a tiny bit miffed about the article, and now says the Journal exaggerated the bonuses paid to certain traders and the profits made by certain departments. That's Goldman's only complaint, however, and so the Journal story is probably true, as far as it goes. The only trouble is that it does not go far enough.

Briefly, the Journal story runs as follows:

By the end of 2006, the people creating and selling sub-prime mortgages and other so-called CDOs (collateralised debt obligations), had put Goldman Sachs in exactly the same position as every other Wall Street firm. Left to their own devices, traders in sub-prime-mortgage bonds would have sunk Goldman just as they sank Merrill Lynch, Citigroup Inc., Bear Stearns Cos. and every other major Wall Street firm.

Enter two smart guys who trade Goldman's proprietary books to argue to the CEO and chief financial officer that the sub-prime market feels soft and that Goldman should short it. This they do, in such massive quantities that they more than offset the long positions in subprime held throughout the rest of the firm, leaving Goldman short the sub-prime market and in a position to make billions when it crashes. End of story.

And it is a good story. But consider what it implies. Their own traders and salespeople in sub-prime mortgages and related securities had put Goldman in exactly the same position as every other Wall Street firm: long sub-prime mortgages.

The only difference between Goldman and everyone else was that Goldman had, in effect, an entirely separate enterprise, sitting on top of the firm, with the power to reverse the judgment of its own supposed experts in various markets. They were able to do this, apparently, without ever saying a word about it to their own traders. Instead of telling the fools trading sub-prime mortgages that they are wrong, and that they should unwind their positions, they simply offset their trades.

All across Wall Street risk managers are being fired, reassigned or hovering under a cloud of contempt and suspicion. Heads must roll, and after the CEO, these guys are the most plausible to guillotine.

Michael Lewis is the author, most recently of "The Blind Side," and is a Bloomberg News columnist. The opinions expressed are his own.