Gretchen Morgenson writes on the roots of the collapse of Merrill Lynch in How the Thundering Herd Faltered and Fell as part of a New York Times series on the financial crisis:

“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.”

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.

… By 2005, with the home lending mania in full swing, the amount of C.D.O.’s holding opaque and risky mortgage assets far exceeded C.D.O.’s composed of blue-chip corporate loans. And inside even more abstract synthetic C.D.O.’s, the risk was harder to parse and much easier to overlook.

Similarly, in the same series on the financial crisis, Eric Dash and Julie Creswell write on the collapse of Citibank in Citigroup Saw No Red Flags Even as It Made Bolder Bets:

… many Citigroup insiders say the bank’s risk managers never investigated deeply enough. Because of longstanding ties that clouded their judgment, the very people charged with overseeing deal makers eager to increase short-term earnings — and executives’ multimillion-dollar bonuses — failed to rein them in, these insiders say.

…While much of the damage inflicted on Citigroup and the broader economy was caused by errant, high-octane trading and lax oversight, critics say, blame also reaches into the highest levels at the bank. Earlier this year, the Federal Reserve took the bank to task for poor oversight and risk controls in a report it sent to Citigroup.

… regulators have criticized the banking industry as a whole for relying on outsiders — in particular the ratings agencies — to help them gauge the risk of their investments.

“There is really no excuse for institutions that specialize in credit risk assessment, like large commercial banks, to rely solely on credit ratings in assessing credit risk,” John C. Dugan, the head of the Office of the Comptroller of the Currency, the chief federal bank regulator, said in a speech earlier this year.