“We have auctioned billions in credit-default swap positions in our C.D.O. liquidation business,” Mr. Farrell said, “and what we have learned is that the carnage we are witnessing now would have been much more contained, to use that overworked word, without credit-default swaps.”

The bankers who invented the synthetics for J. P. Morgan say they kept only the highest-quality and most bulletproof portions of their product in-house, known as the super senior slice. They quickly sold anything riskier to firms that were willing to take on the dangers of ownership in exchange for fatter fees.

“In 1997 and 1998, when we invented super senior risk, we spent a lot of time examining how much is too much to have on our books,” said Blythe Masters, who was on the small team that invented the synthetic C.D.O. and is now head of commodities at JPMorgan Chase. “We would warehouse risk for a period of time, but we were always focused on developing a market for whatever we did. The idea was we were financial intermediaries. We weren’t in the investment business.”

Image In 1997, J. P. Morgan bankers like Blythe Masters, left, and William Winters served on a small team that pioneered synthetic C.D.O.s. Credit... Richard Sheinwald/Bloomberg News, left; Douglas Fry/Cazenove Group, via Bloomberg News

For years, the product that Ms. Masters and her colleagues invented remained just a mechanism for offloading risk in high-grade corporate lending. But as often occurs with Wall Street alchemy, a good idea started to be misused  and a product initially devised to insulate against risk soon morphed into a device that actually concentrated dangers.

This shift began in 2002, when low interest rates pushed investors to seek higher returns.

“Investors said, ‘I don’t want to be in equities anymore and I’m not getting any return in my bond positions,’ ” said William T. Winters, co-chief executive of JPMorgan’s investment bank and a colleague of Ms. Masters on the team that invented the first synthetic. “Two things happened. They took more and more leverage, and they reached for riskier asset classes. Give me yield, give me leverage, give me return.”

A few years ago, of course, some of the biggest returns were being harvested in the riskier reaches of the mortgage market. As C.D.O.’s and other forms of bundled mortgages were pooled nationwide, banks, investors and rating agencies all claimed that the risk of owning such packages was softened because of the broad diversity of loans in each pool.