The S.E.C. focused in the complaint on disclosures in the marketing of Abacus, saying that the sales documents had failed to tell investors that the deal was devised with the help of John A. Paulson, the billionaire hedge fund manager, who was not named in the case. Mr. Paulson’s firm suggested that the deal be linked to mortgages for which he expected a high rate of default, the S.E.C. said; when that came to pass, the bets he placed against the securities proved very profitable for him. But investors on the other side lost more than $1 billion, according to the S.E.C.

Mr. Tourre’s lawyers wrote that their client was “simply one member of a large team that worked on the 2007-AC1 transaction” — referring to the Abacus deal — “and was entitled to rely on Goldman Sachs’s institutional processes to ensure that disclosures were properly drafted.” He was not a lawyer, they argued. Legal counsel on a deal, in this case Mr. Littlejohn and Mr. Gerst, typically review documents and decide what must be disclosed to investors.

The S.E.C. has not said why it focused on just one Abacus deal, even though other mortgage securities created by Goldman and other banks had similar designs and disclosures. In many of the securities, for example, there was an investor like Mr. Paulson or Goldman itself betting against the housing market, and often that party helped devise the deal, according to four former Goldman employees familiar with the securities.

Indeed, there was at least one other security that had involved Mr. Paulson, according to the 2007 memo written by Mr. Tourre’s desk.

It was Mr. Egol’s name that came up most prominently in Mr. Tourre’s legal response to the S.E.C., as well as in interviews with traders knowledgeable about the Abacus deals.

A former colleague on Goldman’s mortgage desk who now works for another financial firm said he did not understand why Mr. Tourre had been singled out. “That has baffled me from the very beginning. I just can’t even begin to tell you how junior and insignificant his role was,” said this person, who asked not to be named because it could damage his career.

Mr. Tourre’s lawyers also pointed to an e-mail that February from Mr. Egol, which said “the cdo biz is dead we don’t have a lot of time left.” The S.E.C. pointed to that line as evidence that Mr. Tourre had known of the trouble in the market. Mr. Tourre’s lawyers responded that those views were Mr. Egol’s and “not necessarily” Mr. Tourre’s.