Wall Street played a crucial role in the mortgage market’s path to collapse. Investment banks bundled mortgage loans into securities and then often rebundled those securities one or two more times. Those securities were given high ratings and sold to investors, who have since lost billions of dollars on them.

Banks were put on notice last summer that investigators of all sorts were looking into their mortgage operations, when requests for information were sent out to all of the big Wall Street firms. The topics of interest included the way mortgage securities were created, marketed and rated and some banks’ own trading against the mortgage market.

The S.E.C.’s civil case against Goldman is the most prominent action so far. But other actions could be taken by the Justice Department, the F.B.I. or the Financial Crisis Inquiry Commission — all of which are looking into the financial crisis. Criminal cases carry a higher burden of proof than civil cases. Under a New York state law, Mr. Cuomo can bring a criminal or civil case.

His office scrutinized the rating agencies back in 2008, just as the financial crisis was beginning. In a settlement, the agencies agreed to demand more information on mortgage bonds from banks.

Mr. Cuomo was also concerned about the agencies’ fee arrangements, which allowed banks to shop their deals among the agencies for the best rating. To end that inquiry, the agencies agreed to change their models so they would be paid for any work they did for banks, even if those banks did not select them to rate a given deal.

Mr. Cuomo’s current focus is on information the investment banks provided to the rating agencies and whether the bankers knew the ratings were overly positive, the people who know of the investigation said.

A Senate subcommittee found last month that Wall Street workers had been intimately involved in the rating process. In one series of e-mail messages the committee released, for instance, a Goldman worker tried to persuade Standard & Poor’s to allow Goldman to handle a deal in a way that the analyst found questionable.